Professional Education
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Ph. D., Harvard University, Biology (1956)
All Publications
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Phototropic solar tracking in sunflower plants: an integrative perspective.
Annals of botany
2016; 117 (1): 1-8
Abstract
One of the best-known plant movements, phototropic solar tracking in sunflower (Helianthus annuus), has not yet been fully characterized. Two questions are still a matter of debate. (1) Is the adaptive significance solely an optimization of photosynthesis via the exposure of the leaves to the sun? (2) Is shade avoidance involved in this process? In this study, these concepts are discussed from a historical perspective and novel insights are provided.Results from the primary literature on heliotropic growth movements led to the conclusion that these responses cease before anthesis, so that the flowering heads point to the East. Based on observations on 10-week-old plants, the diurnal East-West oscillations of the upper fifth of the growing stem and leaves in relation to the position of the sun (inclusive of nocturnal re-orientation) were documented, and photon fluence rates on the leaf surfaces on clear, cloudy and rainy days were determined. In addition, the light-response curve of net CO2 assimilation was determined on the upper leaves of the same batch of plants, and evidence for the occurrence of shade-avoidance responses in growing sunflower plants is summarized.Only elongating, vegetative sunflower shoots and the upper leaves perform phototropic solar tracking. Photon fluence response and CO2 assimilation measurements cast doubt on the 'photosynthesis-optimization hypothesis' as the sole explanation for the evolution of these plant movements. We suggest that the shade-avoidance response, which maximizes light-driven CO2 assimilation, plays a major role in solar tracking populations of competing sunflower plants, and an integrative scheme of these growth movements is provided.
View details for DOI 10.1093/aob/mcv141
View details for PubMedID 26420201
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LOV Histidine Kinase Modulates the General Stress Response System and Affects the virB Operon Expression in Brucella abortus
PLOS ONE
2015; 10 (5)
Abstract
Brucella is the causative agent of the zoonotic disease brucellosis, and its success as an intracellular pathogen relies on its ability to adapt to the harsh environmental conditions that it encounters inside the host. The Brucella genome encodes a sensor histidine kinase containing a LOV domain upstream from the kinase, LOVHK, which plays an important role in light-regulated Brucella virulence. In this report we study the intracellular signaling pathway initiated by the light sensor LOVHK using an integrated biochemical and genetic approach. From results of bacterial two-hybrid assays and phosphotransfer experiments we demonstrate that LOVHK functionally interacts with two response regulators: PhyR and LovR, constituting a functional two-component signal-transduction system. LOVHK contributes to the activation of the General Stress Response (GSR) system in Brucella via PhyR, while LovR is proposed to be a phosphate-sink for LOVHK, decreasing its phosphorylation state. We also show that in the absence of LOVHK the expression of the virB operon is down-regulated. In conclusion, our results suggest that LOVHK positively regulates the GSR system in vivo, and has an effect on the expression of the virB operon. The proposed regulatory network suggests a similar role for LOVHK in other microorganisms.
View details for DOI 10.1371/journal.pone.0124058
View details for Web of Science ID 000354918600007
View details for PubMedID 25993430
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The blue light receptor Phototropin 1 suppresses lateral root growth by controlling cell elongation
PLANT BIOLOGY
2015; 17 (1): 34-40
Abstract
We investigated the relationship between the blue light receptor phototropin 1 (phot1) and lateral root growth in Arabidopsis thaliana seedlings. Fluorescence and confocal microscopy images, as well as PHOT1 mRNA expression studies provide evidence that it is highly expressed in the elongation zone of lateral roots where auxin is accumulating. However, treatment with the auxin transport inhibitor N-1-naphthylphthalamic acid significantly reduced PHOT1 expression in this zone. In addition, PHOT1 expression was higher in darkness than in light. The total number of lateral roots was higher in the phot1 mutant than in wild-type Arabidopsis. Cells in the elongation zone of lateral roots of the phot1 mutant were longer than those of wild-type lateral roots. These findings suggest that PHOT1 plays a role(s) in elongation of lateral roots through the control of an auxin-related signalling pathway.
View details for DOI 10.1111/plb.12187
View details for Web of Science ID 000347707900005
View details for PubMedID 24803136
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COP1 Jointly Modulates Cytoskeletal Processes and Electrophysiological Responses Required for Stomatal Closure.
Molecular plant
2014; 7 (9): 1441-1454
Abstract
Reorganization of the cortical microtubule cytoskeleton is critical for guard cell function. Here, we investigate how environmental and hormonal signals cause these rearrangements and find that COP1, a RING-finger-type ubiquitin E3 ligase, is required for degradation of tubulin, likely by the 26S proteasome. This degradation is required for stomatal closing. In addition to regulating the cytoskeleton, we show that cop1 mutation impaired the activity of S-type anion channels, which are critical for stomatal closure. Thus, COP1 is revealed as a potential coordinator of cytoskeletal and electrophysiological activities required for guard cell function.
View details for DOI 10.1093/mp/ssu065
View details for PubMedID 25151660
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Blue Light-Induced Proteomic Changes in Etiolated Arabidopsis Seedlings
JOURNAL OF PROTEOME RESEARCH
2014; 13 (5): 2524-2533
View details for DOI 10.1021/pr500010z
View details for Web of Science ID 000335490600025
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Phototropism: Some History, Some Puzzles, and a Look Ahead
PLANT PHYSIOLOGY
2014; 164 (1): 13-23
View details for DOI 10.1104/pp.113.230573
View details for Web of Science ID 000329447400002
View details for PubMedID 24399823
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Seedling development in buckwheat and the discovery of the photomorphogenic shade-avoidance response
PLANT BIOLOGY
2013; 15 (6): 931-940
Abstract
Numerous botanists of the early 19th century investigated the effect of sunlight on plant development, but no clear picture developed. One hundred and fifty years ago, Julius Sachs (1863) systematically analysed the light-plant relationships, using developing garden nasturtium (Tropaeolum majus) and seedlings of buckwheat (Fagopyron esculentum) as experimental material. From these studies, Sachs elucidated the phenomenon of photomorphogenesis (plant development under the influence of daylight) and the associated 'shade-avoidance response'. We have reproduced the classical buckwheat experiments of Sachs (1863) and document the original shade-avoidance syndrome with reference to hypocotyl elongation and cotyledon development in darkness (skotomorphogenesis), white light and shade induced by a canopy of green leaves. In subsequent publications, Sachs elaborated his concepts of 1863 and postulated the occurrence of 'flower-inducing substances'. In addition, he argued that the shade-avoidance response in cereals, such as wheat and maize, is responsible for lodging in crowded plant communities. We discuss these processes with respect to the red- to far-red light/phytochrome B relationships. Finally, we summarise the phytochrome B-phytohormone (auxin, brassinosteroids) connection within the cells of shaded Arabidopsis plants, and present a simple model to illustrate the shade-avoidance syndrome. In addition, we address the relationship between plant density and health of the corresponding population, a topic that was raised for the first time by Sachs (1863) in his seminal paper and elaborated in his textbooks.
View details for DOI 10.1111/plb.12077
View details for Web of Science ID 000325984000002
View details for PubMedID 24112603
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SUPPRESSOR OF MORE AXILLARY GROWTH2 1 Controls Seed Germination and Seedling Development in Arabidopsis
PLANT PHYSIOLOGY
2013; 163 (1): 318-330
Abstract
Abiotic chemical signals discovered in smoke that are known as karrikins (KARs) and the endogenous hormone strigolactone (SL) control plant growth through a shared MORE AXILLARY GROWTH2 (MAX2)-dependent pathway. A SL biosynthetic pathway and candidate KAR/SL receptors have been characterized, but signaling downstream of MAX2 is poorly defined. A screen for genetic suppressors of the enhanced seed dormancy phenotype of max2 in Arabidopsis (Arabidopsis thaliana) led to identification of a suppressor of max2 1 (smax1) mutant. smax1 restores the seed germination and seedling photomorphogenesis phenotypes of max2 but does not affect the lateral root formation, axillary shoot growth, or senescence phenotypes of max2. Expression of three transcriptional markers of KAR/SL signaling, D14-LIKE2, KAR-UP F-BOX1, and INDOLE-3-ACETIC ACID INDUCIBLE1, is rescued in smax1 max2 seedlings. SMAX1 is a member of an eight-gene family in Arabidopsis that has weak similarity to HEAT SHOCK PROTEIN 101, which encodes a caseinolytic peptidase B chaperonin required for thermotolerance. SMAX1 and the SMAX1-like (SMXL) homologs are differentially expressed in Arabidopsis tissues. SMAX1 transcripts are most abundant in dry seed, consistent with its function in seed germination control. Several SMXL genes are up-regulated in seedlings treated with the synthetic SL GR24. SMAX1 and SMXL2 transcripts are reduced in max2 seedlings, which could indicate negative feedback regulation by KAR/SL signaling. smax1 seed and seedling growth mimics the wild type treated with KAR/SL, but smax1 seedlings are still responsive to 2H-furo[2,3-c]pyran-2-one (KAR2) or GR24. We conclude that SMAX1 is an important component of KAR/SL signaling during seed germination and seedling growth but is not necessary for all MAX2-dependent responses. We hypothesize that one or more SMXL proteins may also act downstream of MAX2 to control the diverse developmental responses to KARs and SLs.
View details for DOI 10.1104/pp.113.221259
View details for Web of Science ID 000323759200026
View details for PubMedID 23893171
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Investigations on the Photoregulation of Chloroplast Movement and Leaf Positioning in Arabidopsis
PLANT AND CELL PHYSIOLOGY
2013; 54 (1): 48-56
Abstract
We recently investigated the roles of the phototropin 1 (PHOT1) LOV (light, oxygen or voltage) domains in mediating phototropic curvature in transgenic Arabidopsis seedlings expressing either wild-type PHOT1 or PHOT1 with one or both LOV domains inactivated by a single amino acid replacement. We have now investigated the role of the PHOT1 LOV domains in chloroplast movement and in leaf positioning in response to blue light. Low fluence rate blue light is known to mediate a chloroplast accumulation response and high fluence rate blue light an avoidance response in Arabidopsis leaves. As was the case for phototropism, LOV2 of PHOT1 is essential for chloroplast accumulation and LOV1 is dispensable. PHOT1 LOV2 is also essential to maintain developing primary leaves in a horizontal position under white light from above and LOV1 is again dispensable. A red light pulse given to dark-adapted light-grown plants followed by 2 h of darkness enhances both the chloroplast accumulation response under dim blue light and the chloroplast avoidance response under strong blue light. The effect is far-red reversible. This photoreversible response is normal in a phyB null mutant but does not appear in a phyA null mutant. These results suggest that phyA mediates the enhancement, induced by a red light pulse, of blue light-induced chloroplast movements.
View details for DOI 10.1093/pcp/pcs098
View details for Web of Science ID 000315218100005
View details for PubMedID 22782888
View details for PubMedCentralID PMC3539441
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Quantitative Changes in Microtubule Distribution Correlate with Guard Cell Function in Arabidopsis
MOLECULAR PLANT
2012; 5 (3): 716-725
Abstract
Radially arranged cortical microtubules are a prominent feature of guard cells. We observed guard cells expressing GFP-tubulin (GFP-TUA6) with confocal microscopy and found recognizable changes in the appearance of microtubules when stomata open or close (Eisinger et al., 2012). In the present study, analysis of fluorescence distribution showed a dramatic increase in peak intensities of microtubule bundles within guard cells as stomata open. This increase was correlated with an increase in the total fluorescence that could be attributed to polymerized tubulin. Adjacent pavement cells did not show similar changes in peak intensities or integrated fluorescence when stomatal apertures changed. Imaging of RFP-tagged end binding protein 1 (EB1) and YFP-tagged α-tubulin expressed in the same cell revealed that the number of microtubules with growing ends remained constant, although the total amount of polymerized tubulin was higher in open than in closed guard cells. Taken together, these results indicate that the changes in microtubule array organization that are correlated with and required for normal guard cell function are characterized by changes in microtubule clustering or bundling.
View details for DOI 10.1093/mp/sss033
View details for Web of Science ID 000304890600019
View details for PubMedID 22492121
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Microtubules Are Essential for Guard-Cell Function in Vicia and Arabidopsis
MOLECULAR PLANT
2012; 5 (3): 601-610
Abstract
Radially arranged cortical microtubules are a prominent feature of guard cells. Guard cells expressing GFP-tubulin showed consistent changes in the appearance of microtubules when stomata opened or closed. Guard cells showed fewer microtubule structures as stomata closed, whether induced by transfer to darkness, ABA, hydrogen peroxide, or sodium hydrogen carbonate. Guard cells kept in the dark (closed stomata) showed increases in microtubule structures and stomatal aperture on light treatment. GFP-EB1, marking microtubule growing plus ends, showed no change in number of plus ends or velocity of assembly on stomatal closure. Since the number of growing plus ends and the rate of plus-end growth did not change when microtubule structure numbers declined, microtubule instability and/or rearrangement must be responsible for the apparent loss of microtubules. Guard cells with closed stomata showed more cytosolic GFP-fluorescence than those with open stomata as cortical microtubules became disassembled, although with a large net loss in total fluorescence. Microtubule-targeted drugs blocked guard-cell function in Vicia and Arabidopsis. Oryzalin disrupted guard-cell microtubules and prevented stomatal opening and taxol stabilized guard-cell microtubules and delayed stomatal closure. Gas exchange measurements indicated that the transgenes for fluorescent-labeled proteins did not disrupt normal stomatal function. These dynamic changes in guard-cell microtubules combined with our inhibitor studies provide evidence for an active role of microtubules in guard-cell function.
View details for DOI 10.1093/mp/sss002
View details for Web of Science ID 000304890600009
View details for PubMedID 22402260
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The Role of a 14-3-3 Protein in Stomatal Opening Mediated by PHOT2 in Arabidopsis
PLANT CELL
2012; 24 (3): 1114-1126
Abstract
The 14-3-3 λ isoform is required for normal stomatal opening mediated by PHOT2 in Arabidopsis thaliana. Arabidopsis phototropin2 (PHOT2) interacts with the λ-isoform 14-3-3 protein both in yeast two-hybrid screening and in an in vitro pull-down assay. Further yeast two-hybrid analysis also showed that the PHOT2 C-terminal kinase domain was required for the interaction. Site-directed mutagenesis indicated that PHOT2 Ser-747 is essential for the yeast interaction. Phenotypic characterization of a loss-of-function 14-3-3 λ mutant in a phot1 mutant background showed that the 14-3-3 λ protein was necessary for normal PHOT2-mediated blue light-induced stomatal opening. PHOT2 Ser-747 was necessary for complementation of the blue light-activated stomatal response in a phot1 phot2 double mutant. The 14-3-3 λ mutant in the phot1 mutant background allowed normal phototropism and normal chloroplast accumulation and avoidance responses. It also showed normal stomatal opening mediated by PHOT1 in a phot2 mutant background. The 14-3-3 κ mutant had no effect on stomatal opening in response to blue light. Although the 14-3-3 λ mutant had no chloroplast movement phenotype, the 14-3-3 κ mutation caused a weaker avoidance response at an intermediate blue light intensity by altering the balance between the avoidance and accumulation responses. The results highlight the strict specificity of phototropin-mediated signal transduction pathways.
View details for DOI 10.1105/tpc.111.092130
View details for Web of Science ID 000303763000020
View details for PubMedID 22408078
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Root phototropism: from dogma to the mechanism of blue light perception
PLANTA
2012; 235 (3): 443-452
Abstract
In roots, the "hidden half" of all land plants, gravity is an important signal that determines the direction of growth in the soil. Hence, positive gravitropism has been studied in detail. However, since the 19th century, the response of roots toward unilateral light has also been analyzed. Based on studies on white mustard (Sinapis alba) seedlings, botanists have concluded that all roots are negatively phototropic. This "Sinapis-dogma" was refuted in a seminal study on root phototropism published a century ago, where it was shown that less then half of the 166 plant species investigated behave like S. alba, whereas 53% displayed no phototropic response at all. Here we summarize the history of research on root phototropism, discuss this phenomenon with reference to unpublished data on garden cress (Lepidium sativum) seedlings, and describe the effects of blue light on the negative bending response in Thale cress (Arabidopsis thaliana). The ecological significance of root phototropism is discussed and the relationships between gravi- and phototropism are outlined, with respect to the starch-statolith-theory of gravity perception. Finally, we present an integrative model of gravi- and blue light perception in the root tip of Arabidopsis seedlings. This hypothesis is based on our current view of the starch-statolith-concept and light sensing via the cytoplasmic red/blue light photoreceptor phytochrome A and the plasma membrane-associated blue light receptor phototropin-1. Open questions and possible research agendas for the future are summarized.
View details for DOI 10.1007/s00425-012-1597-y
View details for Web of Science ID 000300850900001
View details for PubMedID 22293854
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The Arabidopsis rcn1-1 Mutation Impairs Dephosphorylation of Phot2, Resulting in Enhanced Blue Light Responses
PLANT CELL
2010; 22 (2): 392-402
Abstract
Phototropins (phot) sense blue light through the two N-terminal chromophore binding LOV domains and activate the C-terminal kinase domain. The resulting phototropin autophosphorylation is essential for biological activity. We identified the A1 subunit of Ser/Thr protein phosphatase 2A (PP2A) as interacting with full-length phot2 in yeast and also interacting with phot2 in an in vitro protein binding assay. Phenotypic characterizations of a phot1-5 rcn1-1 (for root curling in n-naphthylphthalamic acid1) double mutant, in which phot2 is the only functional phototropin and PP2A activity is reduced, showed enhanced phototropic sensitivity and enhanced blue light-induced stomatal opening, suggesting that PP2A activity is involved in regulating phot2 function. When treated with cantharidin, a chemical inhibitor of PP2A, the phot1-5 mutant exhibited enhanced phot2-mediated phototropic responses like those of the phot1-5 rcn1-1 double mutant. Immunoblot analysis to examine phot2 endogenous phosphorylation levels and in vitro phosphorylation assays of phot2 extracted from plants during dark recovery from blue light exposure confirmed that phot2 is more slowly dephosphorylated in the reduced PP2A activity background than in the wild-type PP2A background, suggesting that phosphorylated phot2 is a substrate of PP2A activity. While reduced PP2A activity enhanced the activity of phot2, it did not enhance either phot1 dephosphorylation or the activity of phot1 in mediating phototropism or stomatal opening.
View details for DOI 10.1105/tpc.109.066423
View details for Web of Science ID 000275926200011
View details for PubMedID 20139163
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LIGHT-ACTIVATED BACTERIAL LOV-DOMAIN HISTIDINE KINASES
METHODS IN ENZYMOLOGY, VOL 471: TWO-COMPONENT SIGNALING SYSTEMS, PART C
2010; 471: 125-134
Abstract
Bacteria rely on two-component signaling systems in their adaptive responses to environmental changes. Typically, the two-component system consists of a sensory histidine kinase that signals by transferring a phosphoryl group to a secondary response regulator that ultimately relays the signal to the cell. Some of these sensors use PAS (Per-Arnt-Sin) domains. A new member of the PAS super family is the LOV (light, oxygen, voltage) domain, a 10-kDa flavoprotein that functions as a light-sensory module in plant, algal, fungal, and bacterial blue-light receptors. Putative LOV domains have been identified in the genomes of many higher and lower eukaryotes, plants, eubacteria, archaebacteria, and particularly in genes coding for histidine kinases (LOV-histidine kinases, LOV-HKs) of plant and animal pathogenic bacteria, including Brucella. We describe here biochemical, photochemical, and biophysical methodology to purify these enzymes and to characterize their light-activation process.
View details for DOI 10.1016/S0076-6879(10)71008-9
View details for Web of Science ID 000275827600008
View details for PubMedID 20946846
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A Wandering Pathway in Plant Biology: From Wildflowers to Phototropins to Bacterial Virulence
ANNUAL REVIEW OF PLANT BIOLOGY, VOL 61
2010; 61: 1-20
Abstract
The author describes the somewhat convoluted pathway he followed from amateur taxonomy of Minnesota wildflowers to identification of the phototropin family of blue-light receptors. He also mentions individuals who were important in moving his career first into plant taxonomy, then plant development, and finally plant photobiology (and out of music). He emphasizes the many twists and turns a research career can take, including a few that lead to blind ends. He also emphasizes the oscillatory nature of his career-back and forth between the Atlantic and Pacific oceans (with occasional forays to Freiburg, Germany) and back and forth between red-light receptors and blue-light receptors. There is a short intermission in which he describes his longtime relationship with California's Henry W. Coe State Park. Finally, he relates how he followed the unlikely pathway from plant blue-light receptors to a blue-light receptor required to maximize virulence of a bacterial animal pathogen.
View details for DOI 10.1146/annurev-arplant-042809-112326
View details for Web of Science ID 000278924400001
View details for PubMedID 20192732
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From Charles Darwin's botanical country-house studies to modern plant biology
PLANT BIOLOGY
2009; 11 (6): 785-795
Abstract
As a student of theology at Cambridge University, Charles Darwin (1809-1882) attended the lectures of the botanist John S. Henslow (1796-1861). This instruction provided the basis for his life-long interest in plants as well as the species question. This was a major reason why in his book On the Origin of Species, which was published 150 years ago, Darwin explained his metaphorical phrase 'struggle for life' with respect to animals and plants. In this article, we review Darwin's botanical work with reference to the following topics: the struggle for existence in the vegetable kingdom with respect to the phytochrome-mediated shade avoidance response; the biology of flowers and Darwin's plant-insect co-evolution hypothesis; climbing plants and the discovery of action potentials; the power of movement in plants and Darwin's conflict with the German plant physiologist Julius Sachs; and light perception by growing grass coleoptiles with reference to the phototropins. Finally, we describe the establishment of the scientific discipline of Plant Biology that took place in the USA 80 years ago, and define this area of research with respect to Darwin's work on botany and the physiology of higher plants.
View details for DOI 10.1111/j.1438-8677.2009.00243.x
View details for Web of Science ID 000270429300001
View details for PubMedID 19796355
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Role of root UV-B sensing in Arabidopsis early seedling development
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2008; 105 (52): 21039-21044
Abstract
All sun-exposed organisms are affected by UV-B [(UVB) 280-320 nm], an integral part of sunlight. UVB can cause stresses or act as a developmental signal depending on its fluence levels. In plants, the mechanism by which high-fluence-rate UVB causes damages and activates DNA-repair systems has been extensively studied. However, little is known about how nondamaging low-fluence-rate UVB is perceived to regulate plant morphogenesis and development. Here, we report the identification of an Arabidopsis mutant, root UVB sensitive 1 (rus1), whose primary root is hypersensitive to very low-fluence-rate (VLF) UVB. Under standard growth-chamber fluorescent white light, rus1 displays stunted root growth and fails to form postembryonic leaves. Experiments with different monochromatic light sources showed that rus1 phenotypes can be rescued if the seedlings are allowed to grow in light conditions with minimum UVB. We determined that roots, not other organs, perceive the UVB signal. Genetic and molecular analyses confirmed that the root light-sensitive phenotypes are independent of all other known plant photoreceptors. Three rus1 alleles have been identified and characterized. A map-based approach was used to identify the RUS1 locus. RUS1 encodes a protein that contains DUF647 (domain of unknown function 647), a domain highly conserved in eukaryotes. Our results demonstrate a root VLF UVB-sensing mechanism that is involved in Arabidopsis early seedling morphogenesis and development.
View details for DOI 10.1073/pnas.0809942106
View details for Web of Science ID 000262092800084
View details for PubMedID 19075229
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Introduction to the Symposium-in-Print on Photosynthesis
PHOTOCHEMISTRY AND PHOTOBIOLOGY
2008; 84 (6): 1300-1301
View details for DOI 10.1111/j.1751-1097.2008.00463.x
View details for Web of Science ID 000261081200002
View details for PubMedID 19067953
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Phytochrome A Regulates the Intracellular Distribution of Phototropin 1-Green Fluorescent Protein in Arabidopsis thaliana
PLANT CELL
2008; 20 (10): 2835-2847
Abstract
It has been known for decades that red light pretreatment has complex effects on subsequent phototropic sensitivity of etiolated seedlings. Here, we demonstrate that brief pulses of red light given 2 h prior to phototropic induction by low fluence rates of blue light prevent the blue light-induced loss of green fluorescent protein-tagged phototropin 1 (PHOT1-GFP) from the plasma membrane of cortical cells of transgenic seedlings of Arabidopsis thaliana expressing PHOT1-GFP in a phot1-5 null mutant background. This red light effect is mediated by phytochrome A and requires approximately 2 h in the dark at room temperature to go to completion. It is fully far red reversible and shows escape from photoreversibility following 30 min of subsequent darkness. Red light-induced inhibition of blue light-inducible changes in the subcellular distribution of PHOT1-GFP is only observed in rapidly elongating regions of the hypocotyl. It is absent in hook tissues and in mature cells below the elongation zone. We hypothesize that red light-induced retention of the PHOT1-GFP on the plasma membrane may account for the red light-induced increase in phototropic sensitivity to low fluence rates of blue light.
View details for DOI 10.1105/tpc.108.059915
View details for Web of Science ID 000261378600026
View details for PubMedID 18952772
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Phytochrome-driven changes in respiratory electron transport partitioning in soybean (Glycine max. L.) cotyledons
PLANT BIOLOGY
2008; 10 (3): 281-287
Abstract
After it was observed that light induces changes in electron partitioning between the cytochrome and the alternative pathway, the focus interest was directed to assessing what type of photoreceptors are involved and the extent of such modifications. Studies on 5-day-old soybean (Glycine max L.) cotyledons using an oxygen isotope fractionation technique showed that phytochrome is involved in changes in electron partitioning between the cytochrome and the alternative respiratory pathway. A follow-up of a previous study, showing that 5 min of white light caused changes in mitochondrial electron partitioning, demonstrated that while blue light was not involved in any such changes, red light caused a significant shift of electrons toward the alternative pathway. The major shift, observed after 24 h of light, is mainly due to both a decrease in the activity of the cytochrome pathway and an increase in the activity of the alternative pathway. The involvement of a phytochrome receptor was confirmed by demonstration of reversibility by far-red light. The implications of the possible involvement of phytochrome in the regulation of mitochondrial electron transport are discussed.
View details for DOI 10.1111/j.1438-8677.2008.00046.x
View details for Web of Science ID 000255140200001
View details for PubMedID 18426475
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The subcellular localization and blue-light-induced movement of phototropin 1-GFP in etiolated seedlings of Arabidopsis thaliana(W)
MOLECULAR PLANT
2008; 1 (1): 103-117
Abstract
Phototropin 1 (phot1) is a photoreceptor for phototropism, chloroplast movement, stomatal opening, leaf expansion, and solar tracking in response to blue light. Following earlier work with PHOT1::GFP (Sakamoto and Briggs, 2002), we investigated the pattern of cellular and subcellular localization of phot1 in 3- 4-d-old etiolated seedlings of Arabidopsis thalinana. As expressed from native upstream sequences, the PHOT1::GFP fusion protein is expressed strongly in the abaxial tissues of the cotyledons and in the elongating regions of the hypocotyl. It is moderately expressed in the shoot/root transition zone and in cells near the root apex. A fluorescence signal is undetectable in the root epidermis, root cap, and root apical meristem itself. The plasma membranes of mesophyll cells near the cotyledon margin appear labeled uniformly but cross-walls created by recent cell divisions are more strongly labeled. The pattern of labeling of individual cell types varies with cell type and developmental stage. Blue-light treatment causes PHOT1::GFP, initially relatively evenly distributed at the plasma membrane, to become reorganized into a distinct mosaic with strongly labeled punctate areas and other areas completely devoid of fluorescence--a phenomenon best observed in cortical cells in the hypocotyl elongation region. Concomitant with or following this reorganization, PHOT1::GFP moves into the cytoplasm in all cell types investigated except for guard cells. It disappears from the cytoplasm by an unidentified mechanism after several hours in darkness. Neither its appearance in the cytoplasm nor its eventual disappearance in darkness is prevented by the translation inhibitor cycloheximide, although the latter process is retarded. We hypothesize that blue-light-induced phot1 re-localization modulates blue-light-activated signal transduction.
View details for DOI 10.1093/mp/ssm011
View details for Web of Science ID 000259068900011
View details for PubMedID 20031918
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Blue-light-activated histidine kinases: Two-component sensors in bacteria
SCIENCE
2007; 317 (5841): 1090-1093
Abstract
Histidine kinases, used for environmental sensing by bacterial two-component systems, are involved in regulation of bacterial gene expression, chemotaxis, phototaxis, and virulence. Flavin-containing domains function as light-sensory modules in plant and algal phototropins and in fungal blue-light receptors. We have discovered that the prokaryotes Brucella melitensis, Brucella abortus, Erythrobacter litoralis, and Pseudomonas syringae contain light-activated histidine kinases that bind a flavin chromophore and undergo photochemistry indicative of cysteinyl-flavin adduct formation. Infection of macrophages by B. abortus was stimulated by light in the wild type but was limited in photochemically inactive and null mutants, indicating that the flavin-containing histidine kinase functions as a photoreceptor regulating B. abortus virulence.
View details for DOI 10.1126/science.1144306
View details for Web of Science ID 000248946700047
View details for PubMedID 17717187
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Steric interactions stabilize the signaling state of the LOV2 domain of phototropin 1
BIOCHEMISTRY
2007; 46 (32): 9310-9319
Abstract
Phototropins (phot1 and phot2) are blue light receptor kinases that control a range of photoresponses that serve to optimize the photosynthetic efficiency of plants. Light sensing by the phototropins is mediated by a repeated motif at the N-terminal region of the protein known as the LOV domain. Bacterially expressed LOV domains bind flavin mononucleotide noncovalently and are photochemically active in solution. Irradiation of the LOV domain results in the formation of a flavin-cysteinyl adduct (LOV390) which thermally relaxes back to the ground state in the dark, effectively completing a photocycle that serves as a molecular switch to control receptor kinase activity. We have employed a random mutagenesis approach to identify further amino acid residues involved in LOV-domain photochemistry. Escherichia coli colonies expressing a mutagenized population of LOV2 derived from Avena sativa (oat) phot1 were screened for variants that showed altered photochemical reactivity in response to blue light excitation. One variant showed slower rates of LOV390 formation but exhibited adduct decay times 1 order of magnitude faster than wild type. A single Ile --> Val substitution was responsible for the effects observed, which removes a single methyl group found in van der Waals contact with the cysteine sulfur involved in adduct formation. A kinetic acceleration trend was observed for adduct decay by decreasing the size of the isoleucine side chain. Our findings therefore indicate that the steric nature of this amino acid side chain contributes to stabilization of the C-S cysteinyl adduct.
View details for DOI 10.1021/bi700852w
View details for Web of Science ID 000248728100016
View details for PubMedID 17658895
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The LOV domain: a chromophore module servicing multiple photoreceptors
Symposium on Molecular Biology in the 21st Century
BIOMED CENTRAL LTD. 2007: 499–504
Abstract
Three different families of blue-light receptors have been characterized from higher plants: three cryptochromes, two phototropins, and the three members of the ZTL/ADO family. Phototropins and the ZTL/ADO proteins have chromophore modules, designated LOV domains, that bind flavin mononucleotide and undergo formation of a C(4a) flavin-cysteinyl adduct. All contain the highly conserved amino acid motif GXNCRFLQ. Over 90 prokaryote proteins also contain LOV domains with this motif upstream from one of several different functional groups. All of these that have been investigated to date act as photoreceptors in vitro and form the adduct upon irradiation. Four members of the class LOV-histidine kinase, one from a plant pathogen (Pseudomonas syringae), one from an animal pathogen Brucella melitensis), and two from a marine bacterium (Erythrobacter litoralis) respectively, mediate light-activated histidine phosphorylation. Decay of the adduct in darkness after a blue light pulse coincides with loss of the capacity for phosphorylation upon addition of ATP. At present, the biological role(s) of these light-sensitive proteins is under investigation.
View details for DOI 10.1007/s11373-007-9162-6
View details for Web of Science ID 000248051500008
View details for PubMedID 17380429
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Physiological roles of the light, oxygen, or voltage domains of phototropin 1 and phototropin 2 in Arabidopsis
PLANT PHYSIOLOGY
2007; 143 (1): 517-529
Abstract
Phototropins (phot1 and phot2) are plant blue-light receptors that mediate phototropism, chloroplast movement, stomatal opening, rapid inhibition of growth of etiolated seedlings, and leaf expansion in Arabidopsis (Arabidopsis thaliana). Their N-terminal region contains two light, oxygen, or voltage (LOV) domains, which bind flavin mononucleotide and form a covalent adduct between a conserved cysteine and the flavin mononucleotide chromophore upon photoexcitation. The C-terminal region contains a serine/threonine kinase domain that catalyzes blue-light-activated autophosphorylation. Here, we have transformed the phot1 phot2 (phot1-5 phot2-1) double mutant with PHOT expression constructs driven by the cauliflower mosaic virus 35S promoter. These constructs encode either wild-type phototropin or phototropin with one or both LOV-domain cysteines mutated to block their photochemistry. We selected multiple lines in each of the eight resulting categories of transformants for further physiological analyses. Specifically, we investigated whether LOV1 and LOV2 serve the same or different functions for phototropism and leaf expansion. Our results show that the LOV2 domain of phot1 plays a major role in phototropism and leaf expansion, as does the LOV2 domain of phot2. No complementation of phototropism or leaf expansion was observed for the LOV1 domain of phot1. However, phot2 LOV1 was unexpectedly found to complement phototropism to a considerable level. Similarly, transformants carrying a PHOT transgene with both LOV domains inactivated developed strong curvatures toward high fluence rate blue light. However, we found that the phot2-1 mutant is leaky and produces a small level of full-length phot2 protein. In vitro experiments indicate that cross phosphorylation can occur between functional phot2 and inactivated phot1 molecules. Such a mechanism may occur in vivo and therefore account for the functional activities observed in the PHOT transgenics with both lov domains inactivated. The implications of this mechanism with respect to phototropin function are discussed.
View details for DOI 10.1104/pp.106.089839
View details for Web of Science ID 000243350600046
View details for PubMedID 17085510
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Phototropins and their LOV domains: Versatile plant blue-light receptors
Conference on Frontiers of Plant Molecular Biology
WILEY-BLACKWELL. 2007: 4–10
View details for DOI 10.1111/j.1744-7909.2006.00406.x
View details for Web of Science ID 000243296200003
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LOV domain-containing proteins in Arabidopsis
58th Yamada Conference on Light Sensing and Signal Transduction in Plant Photomorphogenesis
SPRINGER-VERLAG TOKYO. 2005: 163–169
View details for Web of Science ID 000228726300018
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Epilogue: Eighteen years of progress in photomorphogenesis
58th Yamada Conference on Light Sensing and Signal Transduction in Plant Photomorphogenesis
SPRINGER-VERLAG TOKYO. 2005: 357–362
View details for Web of Science ID 000228726300042
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Phototropin overview
58th Yamada Conference on Light Sensing and Signal Transduction in Plant Photomorphogenesis
SPRINGER-VERLAG TOKYO. 2005: 139–146
View details for Web of Science ID 000228726300015
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Proton transfer reactions in LOV-domain photochemistry
58th Yamada Conference on Light Sensing and Signal Transduction in Plant Photomorphogenesis
SPRINGER-VERLAG TOKYO. 2005: 147–154
View details for Web of Science ID 000228726300016
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FKF1 is essential for photoperiodic-specific light signalling in Arabidopsis
NATURE
2003; 426 (6964): 302-306
Abstract
Adaptation to seasonal change is a crucial component of an organism's survival strategy. To monitor seasonal variation, organisms have developed the capacity to measure day length (photoperiodism). Day-length assessment involves the photoperiodic control of flowering in Arabidopsis thaliana, whereby the coincidence of light and high expression of CONSTANS (CO) induces the expression of FLOWERING LOCUS T (FT), leading to flowering in long-day conditions. Although controlling CO expression is clearly a key step in day-length discrimination, the mechanism that generates day-length-dependent CO expression remains unknown. Here we show that the clock-controlled FLAVIN-BINDING, KELCH REPEAT, F-BOX (FKF1) protein has an essential role in generating the diurnal CO peak and that this function is dependent on light. We show that a recombinant FKF1 LIGHT, OXYGEN OR VOLTAGE (LOV) domain binds the chromophore flavin mononucleotide and undergoes light-induced photochemistry, indicating that FKF1 may function as a photoperiodic blue-light receptor. It is likely that the circadian control of FKF1 expression and the light regulation of FKF1 function coincide to control the daytime CO waveform precisely, which in turn is crucial for day-length discrimination by Arabidopsis.
View details for DOI 10.1038/nature02090
View details for Web of Science ID 000186660800047
View details for PubMedID 14628054
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A carnation anthocyanin mutant is complemented by the glutathione S-transferases encoded by maize Bz2 and petunia An9
PLANT CELL REPORTS
2003; 21 (9): 900-904
Abstract
Particle bombardment was used to elucidate the function of Flavonoid3, a late-acting anthocyanin gene of the ornamental plant, carnation ( Dianthus caryophyllus L.). The fl3 mutation conditions dilute anthocyanin coloration that closely resembles phenotypes produced by the anthocyanin mutants bz2 of maize and an9 of petunia. Bz2 and An9 encode glutathione S-transferases (GSTs) involved in vacuolar sequestration of anthocyanins. Constructs containing either of these or another late-function maize gene, Bronze1 (UDPglucose:flavonol 3- O-glucosyltransferase), were introduced via microprojectile bombardment into fl3 petals. Complementation resulted only from Bz2 and An9, indicating that Fl3 encodes a GST involved in the transport of anthocyanins to the vacuole. The observed result in carnation, an angiosperm phylogenetically distant from maize and petunia, indicates that GST activity might be a universal step in the anthocyanin pathway. Microprojectile bombardment was used to identify late-pathway anthocyanin mutations, which may be responsible for the pale anthocyanin coloration of important cultivars in many species but which can be difficult to characterize by other means.
View details for DOI 10.1007/s00299-002-0545-x
View details for Web of Science ID 000183691300010
View details for PubMedID 12789508
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Intramolecular proton transfers and structural changes during the photocycle of the LOV2 domain of phototropin 1
JOURNAL OF BIOLOGICAL CHEMISTRY
2003; 278 (2): 724-731
Abstract
The phototropins are a family of membrane-associated flavoproteins that function as the primary blue light receptors regulating phototropism, chloroplast movements, stomatal opening, and leaf expansion in plants. Phot1, a member of this family, contains two FMN-binding domains, LOV1 and LOV2, within the N-terminal region and a C-terminal serine-threonine protein kinase domain. Light irradiation of oat phot1 LOV2 produces a cysteinyl adduct (Cys-39) at the flavin C(4a) position, which decays thermally back to the dark state. We measured pH and isotope effects on the photocycle. Between pH 3.7 and 9.5, adduct formation showed minimal pH dependence, and adduct decay showed only slight pH dependence, indicating that the pK values of mechanistically relevant groups are outside this range. LOV2 showed a nearly 5-fold slowing of adduct formation in D(2)O relative to H(2)O, indicating that the rate-limiting step involves proton transfer(s). Light-induced changes in the far UV CD spectrum of LOV2 revealed putative protein structural perturbations. The light minus dark CD difference spectrum resembles an inverted alpha-helix spectrum, suggesting that alpha-helicity is reversibly lost upon light irradiation. Decay kinetics for CD spectral changes in the far UV region occur at the same rate as those in the visible region, indicating synchronous relaxation of protein and chromophore structures.
View details for DOI 10.1074/jbc.M209119200
View details for Web of Science ID 000180321900006
View details for PubMedID 12411437
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Phototropin LOV domains exhibit distinct roles in regulating photoreceptor function
PLANT JOURNAL
2002; 32 (2): 205-219
Abstract
Phototropins (phot1 and phot2) are autophosphorylating serine/threonine kinases that function as photoreceptors for phototropism, light-induced chloroplast movement, and stomatal opening in Arabidopsis. The N-terminal region of phot1 and phot2 contains two specialized PAS domains, designated LOV1 and LOV2, which function as binding sites for the chromophore flavin mononucleotide (FMN). Both LOV1 and LOV2 undergo a self-contained photocycle, which involves the formation of a covalent adduct between the FMN chromophore and a conserved active-site cysteine residue (Cys39). Replacement of Cys39 with alanine abolishes the light-induced photochemical reaction of LOV1 and LOV2. Here we have used the Cys39Ala mutation to investigate the role of LOV1 and LOV2 in regulating phototropin function. Photochemical analysis of a bacterially expressed LOV1 + LOV2 fusion protein indicates that LOV2 functions as the predominant light-sensing domain for phot1. LOV2 also plays a major role in mediating light-dependent autophosphorylation of full-length phot1 expressed in insect cells and transgenic Arabidopsis. Moreover, photochemically active LOV2 alone in full-length phot1 is sufficient to elicit hypocotyl phototropism in transgenic Arabidopsis, whereas photochemically active LOV1 alone is not. Further photochemical and biochemical analyses also indicate that the LOV1 and LOV2 domains of phot2 exhibit distinct roles. The significance for the different roles of the phototropin LOV domains is discussed.
View details for Web of Science ID 000178605000007
View details for PubMedID 12383086
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Cellular and subcellular localization of phototropin 1
PLANT CELL
2002; 14 (8): 1723-1735
Abstract
Phototropin 1 (phot1) is a Ser/Thr photoreceptor kinase that binds two molecules of flavin mononucleotide as its chromophores and undergoes autophosphorylation in response to blue light. Phot1 is plasma membrane associated and, as with phot2, has been shown to function as a photoreceptor for phototropism, blue light-induced chloroplast movement, and blue light-induced stomatal opening. Phot1 likely also plays a redundant role with phot2 in regulating the rate of leaf expansion. Understanding the mechanism(s) by which phot1 initiates these four different responses requires, at minimum, knowledge of where the photoreceptor is located. Therefore, we transformed a phot1 null mutant of Arabidopsis with a construct encoding translationally fused phot1-green fluorescent protein (GFP) under the control of the endogenous PHOT1 promoter and investigated its cellular and subcellular distribution. This PHOT1-GFP construct complements the mutant phenotype, restoring second positive curvature. Phot1 is expressed strongly in dividing and elongating cortical cells in the apical hook and in the root elongation zone in etiolated seedlings. It is localized evenly to the plasma membrane region in epidermal cells but is confined largely to the plasma membrane region of the transverse cell walls in the cortical cells of both root and hypocotyl. It is found at both apical and basal ends of these cortical cells. In light-grown plants, phot1-GFP is localized largely in the plasma membrane regions adjacent to apical and basal cell end walls in the elongating inflorescence stem, where the photoreceptor is expressed strongly in the vascular parenchyma and leaf vein parenchyma. Phot1 also is localized to the plasma membrane region of leaf epidermal cells, mesophyll cells, and guard cells, where its distribution is uniform. Although phot1 is localized consistently to the plasma membrane region in etiolated seedlings, a fraction becomes released to the cytoplasm in response to blue light. Possible relationships between observed phot1 distribution and the various physiological responses activated by blue light are discussed.
View details for DOI 10.1105/tpc.003293
View details for Web of Science ID 000177604700005
View details for PubMedID 12172018
View details for PubMedCentralID PMC151461
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Vibration spectroscopy reveals light-induced chromophore and protein structural changes in the LOV2 domain of the plant blue-light receptor phototropin 1
BIOCHEMISTRY
2002; 41 (23): 7183-7189
Abstract
Phototropins (phot1 and phot2), the plant blue-light receptors for phototropism, chloroplast movement, and stomatal opening, are flavoproteins that contain two approximately 12 kDa FMN-binding domains, LOV1 and LOV2, at their N-terminus, and a serine/threonine protein kinase domain at their C-terminus. The light-activated LOV2 domain forms a metastable intermediate which has been shown to be a protein-chromophore cysteinyl adduct (Cys39) at C(4a) of FMN. This species thermally relaxes back to the ground state in the dark. We measured the light-minus-dark FTIR difference spectra for the LOV2 domain of oat phot1. These spectra show the disappearance of bands at 1580, 1550, and 1350 cm(-1) that originate from, or are strongly coupled to, the N5=C(4a) stretching vibrations, consistent with the perturbations expected upon C(4a) adduct formation. Assignment of these negative difference FTIR bands to native chromophore vibrations is based on the alignment with resonance Raman bands of FMN. Prominent positive bands include a doublet at 1516 and 1536 cm(-1) and one at 1375 and 1298 cm(-1). Normal-mode vibrational-frequency calculations for both lumiflavin and lumiflavin with a sulfur attached at the C(4a) position agree with many of the positive and negative bands observed in the difference spectra. Both calculated and experimental difference FTIR spectra for deuterium isotope substitutions at exchangeable positions in the flavin chromophore are consistent with the assignment of the above positive bands to vibrational modes involving both the newly formed tetrahedral geometry of C(4a) and the N5-H bond in the long-lived LOV2(S)(390) cysteinyl species.
View details for DOI 10.1021/bi025861u
View details for Web of Science ID 000176057300001
View details for PubMedID 12044148
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Photochemical properties of the flavin mononucleotide-binding domains of the phototropins from Arabidopsis, rice, and Chlamydomonas reinhardtii
PLANT PHYSIOLOGY
2002; 129 (2): 762-773
Abstract
Phototropins (phot1 and phot2, formerly designated nph1 and npl1) are blue-light receptors that mediate phototropism, blue light-induced chloroplast relocation, and blue light-induced stomatal opening in Arabidopsis. Phototropins contain two light, oxygen, or voltage (LOV) domains at their N termini (LOV1 and LOV2), each a binding site for the chromophore flavin mononucleotide (FMN). Their C termini contain a serine/threonine protein kinase domain. Here, we examine the kinetic properties of the LOV domains of Arabidopsis phot1 and phot2, rice (Oryza sativa) phot1 and phot2, and Chlamydomonas reinhardtii phot. When expressed in Escherichia coli, purified LOV domains from all phototropins examined bind FMN tightly and undergo a self-contained photocycle, characterized by fluorescence and absorption changes induced by blue light (T. Sakai, T. Kagawa, M. Kasahara, T.E. Swartz, J.M. Christie, W.R. Briggs, M. Wada, K. Okada [2001] Proc Natl Acad Sci USA 98: 6969-6974; M. Salomon, J.M. Christie, E. Knieb, U. Lempert, W.R. Briggs [2000] Biochemistry 39: 9401-9410). The photocycle involves the light-induced formation of a cysteinyl adduct to the C(4a) carbon of the FMN chromophore, which subsequently breaks down in darkness. In each case, the relative quantum efficiencies for the photoreaction and the rate constants for dark recovery of LOV1, LOV2, and peptides containing both LOV domains are presented. Moreover, the data obtained from full-length Arabidopsis phot1 and phot2 expressed in insect cells closely resemble those obtained for the tandem LOV-domain fusion proteins expressed in E. coli. For both Arabidopsis and rice phototropins, the LOV domains of phot1 differ from those of phot2 in their reaction kinetic properties and relative quantum efficiencies. Thus, in addition to differing in amino acid sequence, the phototropins can be distinguished on the basis of the photochemical cycles of their LOV domains. The LOV domains of C. reinhardtii phot also undergo light-activated spectral changes consistent with cysteinyl adduct formation. Thus, the phototropin family extends over a wide evolutionary range from unicellular algae to higher plants.
View details for DOI 10.1104/pp.002410
View details for Web of Science ID 000176363800032
View details for PubMedID 12068117
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Phototropins 1 and 2: versatile plant blue-light receptors
TRENDS IN PLANT SCIENCE
2002; 7 (5): 204-210
Abstract
Blue and ultraviolet-A light regulate a wide range of responses in plants, including phototropism, chloroplast migration and stomatal opening. However, the photoreceptors for these light responses have been identified only recently. The phototropins (phot1 and phot2) represent a new class of receptor kinases that appear to be exclusive to plants. Recent genetic analysis has shown that phot1 and phot2 exhibit partially overlapping functions in mediating phototropism, chloroplast migration, and stomatal opening in Arabidopsis. Although significant progress has been made in understanding the early photochemical and biochemical events that follow phototropin excitation, the details of how this excitation activates such different responses remain to be elucidated.
View details for Web of Science ID 000175361600007
View details for PubMedID 11992825
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Phototropins: A new family of flavin-binding blue light receptors in plants
ANTIOXIDANTS & REDOX SIGNALING
2001; 3 (5): 775-788
Abstract
Phototropin is the designation originally assigned to a recently characterized chromoprotein that serves as a photoreceptor for phototropism. Phototropin is a light-activated autophosphorylating serine/threonine kinase that binds two flavin mononucleotide (FMN) molecules that function as blue light-absorbing chromophores. Each FMN molecule is bound in a rigid binding pocket within specialized PAS (PER-ARNT-SIM superfamily) domains, known as LOV (light, oxygen, or voltage) domains. This article reviews the detailed photobiological and biochemical characterization of the light-activated phosphorylation reaction of phototropin and follows the sequence of events leading to the cloning, sequencing, and characterization of the gene and the subsequent biochemical characterization of its encoded protein. It then considers recent biochemical and photochemical evidence that light activation of phototropin involves the formation of a cysteinyl adduct at the C(4a) position of the FMN chromophores. Adduct formation causes a major conformational change in the chromophores and a possible conformational change in the protein moiety as well. The review concludes with a brief discussion of the evidence for a second phototropin-like protein in Arabidopsis and rice. Possible roles for this photoreceptor are discussed.
View details for Web of Science ID 000174499300007
View details for PubMedID 11761327
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The photocycle of a flavin-binding domain of the blue light photoreceptor phototropin
JOURNAL OF BIOLOGICAL CHEMISTRY
2001; 276 (39): 36493-36500
Abstract
The plant blue light receptor, phot1, a member of the phototropin family, is a plasma membrane-associated flavoprotein that contains two ( approximately 110 amino acids) flavin-binding domains, LOV1 and LOV2, within its N terminus and a typical serine-threonine protein kinase domain at its C terminus. The LOV (light, oxygen, and voltage) domains belong to the PAS domain superfamily of sensor proteins. In response to blue light, phototropins undergo autophosphorylation. E. coli-expressed LOV domains bind riboflavin-5'-monophosphate, are photochemically active, and have major absorption peaks at 360 and 450 nm, with the 450 nm peak having vibronic structure at 425 and 475 nm. These spectral features correspond to the action spectrum for phototropism in higher plants. Blue light excitation of the LOV2 domain generates, in less than 30 ns, a transient approximately 660 nm-absorbing species that spectroscopically resembles a flavin triplet state. This putative triplet state subsequently decays with a 4-micros time constant into a 390 nm-absorbing metastable form. The LOV2 domain (450 nm) recovers spontaneously with half-times of approximately 50 s. It has been shown that the metastable species is likely a flavin-cysteine (Cys(39) thiol) adduct at the flavin C(4a) position. A LOV2C39A mutant generates the early photoproduct but not the adduct. Titrations of LOV2 using chromophore fluorescence as an indicator suggest that Cys(39) exists as a thiolate.
View details for Web of Science ID 000171194500060
View details for PubMedID 11443119
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Arabidopsis nph1 and npl1: Blue light receptors that mediate both phototropism and chloroplast relocation
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
2001; 98 (12): 6969-6974
Abstract
UV-A/blue light acts to regulate a number of physiological processes in higher plants. These include light-driven chloroplast movement and phototropism. The NPH1 gene of Arabidopsis encodes an autophosphorylating protein kinase that functions as a photoreceptor for phototropism in response to low-intensity blue light. However, nph1 mutants have been reported to exhibit normal phototropic curvature under high-intensity blue light, indicating the presence of an additional phototropic receptor. A likely candidate is the nph1 homologue, npl1, which has recently been shown to mediate the avoidance response of chloroplasts to high-intensity blue light in Arabidopsis. Here we demonstrate that npl1, like nph1, noncovalently binds the chromophore flavin mononucleotide (FMN) within two specialized PAS domains, termed LOV domains. Furthermore, when expressed in insect cells, npl1, like nph1, undergoes light-dependent autophosphorylation, indicating that npl1 also functions as a light receptor kinase. Consistent with this conclusion, we show that a nph1 npl1 double mutant exhibits an impaired phototropic response under both low- and high-intensity blue light. Hence, npl1 functions as a second phototropic receptor under high fluence rate conditions and is, in part, functionally redundant to nph1. We also demonstrate that both chloroplast accumulation in response to low-intensity light and chloroplast avoidance movement in response to high-intensity light are lacking in the nph1 npl1 double mutant. Our findings therefore indicate that nph1 and npl1 show partially overlapping functions in two different responses, phototropism and chloroplast relocation, in a fluence rate-dependent manner.
View details for Web of Science ID 000169151500079
View details for PubMedID 11371609
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The phototropin family of photoreceptors
PLANT CELL
2001; 13 (5): 993-997
View details for Web of Science ID 000169030000002
View details for PubMedID 11424903
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Blue light sensing in higher plants
JOURNAL OF BIOLOGICAL CHEMISTRY
2001; 276 (15): 11457-11460
View details for Web of Science ID 000168081800004
View details for PubMedID 11279226
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Photoreceptors in plant photomorphogenesis to date. Five phytochromes, two cryptochromes, one phototropin, and one superchrome
PLANT PHYSIOLOGY
2001; 125 (1): 85-88
View details for Web of Science ID 000167544600021
View details for PubMedID 11154303
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Photochemical and mutational analysis of the FMN-binding domains of the plant blue light receptor, phototropin
BIOCHEMISTRY
2000; 39 (31): 9401-9410
Abstract
The plant photoreceptor phototropin is an autophosphorylating serine-threonine protein kinase activated by UV-A/blue light. Two domains, LOV1 and LOV2, members of the PAS domain superfamily, mediate light sensing by phototropin. Heterologous expression studies have shown that both domains function as FMN-binding sites. Although three plant blue light photoreceptors, cry1, cry2, and phototropin, have been identified to date, the photochemical reactions underlying photoactivation of these light sensors have not been described so far. Herein, we demonstrate that the LOV domains of Avena sativa phototropin undergo a self-contained photocycle characterized by a loss of blue light absorbance in response to light and a spontaneous recovery of the blue light-absorbing form in the dark. Rate constants and quantum efficiencies for the photoreactions indicate that LOV1 exhibits a lower photosensitivity than LOV2. The spectral properties of the photoproduct produced for both LOV domains are unrelated to those found for photoreduced flavins and flavoproteins, but are consistent with those of a flavin-cysteinyl adduct. Flavin-thiol adducts are generally short-lifetime reaction intermediates formed during the flavoprotein-catalyzed reduction of protein disulfides. By site-directed mutagenesis, we have identified several amino acid residues within the putative chromophore binding site of LOV1 and LOV2 that appear to be important for FMN binding and/or the photochemical reactivity. Among those is Cys39, which plays an important role in the photochemical reaction of the LOV domains. Replacement of Cys39 with Ala abolished the photochemical reactions of both LOV domains. We therefore propose that light sensing by the phototropin LOV domains occurs via the formation of a stable adduct between the FMN chromophore and Cys39.
View details for DOI 10.1021/bi000585+
View details for Web of Science ID 000088593300038
View details for PubMedID 10924135
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LOV (light, oxygen, or voltage) domains of the blue-light photoreceptor phototropin (nph1): Binding sites for the chromophore flavin mononucleotide
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1999; 96 (15): 8779-8783
Abstract
Phototropism, the bending response of plant organs to or away from a directional light source, is one of the best studied blue light responses in plants. Although phototropism has been studied for more than a century, recent advances have improved our understanding of the underlying signaling mechanisms involved. The NPH1 gene of Arabidopsis thaliana encodes a blue light-dependent autophosphorylating protein kinase with the properties of a photoreceptor for phototropism. NPH1 apoprotein noncovalently binds FMN to form the holoprotein nph1. The N-terminal region of the protein contains two LOV (light, oxygen, or voltage) domains that share homology with sensor proteins from a diverse group of organisms. These include the bacterial proteins NIFL and AER, both of which bind FAD, and the phy3 photoreceptor from Adiantium capillus-veneris. The LOV domain has therefore been proposed to reflect a flavin-binding site, regulating nph1 kinase activity in response to blue light-induced redox changes. Herein we demonstrate that the LOV domains of two nph1 proteins and phy3 bind stoichiometric amounts of FMN when expressed in Escherichia coli. The spectral properties of the chromopeptides are similar to the action spectrum for phototropism, implying that the LOV domain binds FMN to function as a light sensor. Thus, our findings support the earlier model that nph1 is a dual-chromophoric flavoprotein photoreceptor regulating phototropic responses in higher plants. We therefore propose the name phototropin to designate the nph1 holoprotein.
View details for Web of Science ID 000081589400089
View details for PubMedID 10411952
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Arabidopsis contains at least four independent blue-light-activated signal transduction pathways
PLANT PHYSIOLOGY
1999; 120 (2): 605-614
Abstract
We have investigated the stomatal and phototropic responses to blue light of a number of single and double mutants at various loci that encode proteins involved in blue-light responses in Arabidopsis. The stomatal responses of light-grown mutant plants (cry1, cry2, nph1, nph3, nph4, cry1cry2, and nph1cry1) did not differ significantly from those of their wild-type counterparts. Second positive phototropic responses of etiolated mutant seedlings, cry1, cry2, cry1cry2, and npq1-2, were also similar to those of their wild-type counterparts. Although npq1 and single and double cry1cry2 mutants showed somewhat reduced amplitude for first positive phototropism, threshold, peak, and saturation fluence values for first positive phototropic responses of etiolated seedlings did not differ from those of wild-type seedlings. Similar to the cry1cry2 double mutants and to npq1-2, a phyAphyB mutant showed reduced curvature but no change in the position or shape of the fluence-response curve. By contrast, the phototropism mutant nph1-5 failed to show phototropic curvature under any of the irradiation conditions used in the present study. We conclude that the chromoproteins cry1, cry2, nph1, and the blue-light photoreceptor for the stomatal response are genetically separable. Moreover, these photoreceptors appear to activate separate signal transduction pathways.
View details for Web of Science ID 000080936500029
View details for PubMedID 10364413
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Blue-light photoreceptors in higher plants
ANNUAL REVIEW OF CELL AND DEVELOPMENTAL BIOLOGY
1999; 15: 33-62
Abstract
In the past few years great progress has been made in identifying and characterizing plant photoreceptors active in the blue/UV-A regions of the spectrum. These photoreceptors include cryptochrome 1 and cryptochrome 2, which are similar in structure and chromophore composition to the prokaryotic DNA photolyases. However, they have a C-terminal extension that is not present in photolyases and lack photolyase activity. They are involved in regulation of cell elongation and in many other processes, including interfacing with circadian rhythms and activating gene transcription. Animal cryptochromes that play a photoreceptor role in circadian rhythms have also been characterized. Phototropin, the protein product of the NPH1 gene in Arabidopsis, likely serves as the photoreceptor for phototropism and appears to have no other role. A plasma membrane protein, it serves as photoreceptor, kinase, and substrate for light-activated phosphorylation. The carotenoid zeaxanthin may serve as the chromophore for a photoreceptor involved in blue-light-activated stomatal opening. The properties of these photoreceptors and some of the downstream events they are known to activate are discussed.
View details for Web of Science ID 000085467900002
View details for PubMedID 10611956
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Arabidopsis NPH1: A flavoprotein with the properties of a photoreceptor for phototropism
SCIENCE
1998; 282 (5394): 1698-1701
Abstract
The NPH1 gene of Arabidopsis thaliana encodes a 120-kilodalton serine-threonine protein kinase hypothesized to function as a photoreceptor for phototropism. When expressed in insect cells, the NPH1 protein is phosphorylated in response to blue light irradiation. The biochemical and photochemical properties of the photosensitive protein reflect those of the native protein in microsomal membranes. Recombinant NPH1 noncovalently binds flavin mononucleotide, a likely chromophore for light-dependent autophosphorylation. The fluorescence excitation spectrum of the recombinant protein is similar to the action spectrum for phototropism, consistent with the conclusion that NPH1 is an autophosphorylating flavoprotein photoreceptor mediating phototropic responses in higher plants.
View details for Web of Science ID 000077246600044
View details for PubMedID 9831559
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Arabidopsis NPH1: A protein kinase with a putative redox-sensing domain
SCIENCE
1997; 278 (5346): 2120-2123
Abstract
The NPH1 (nonphototropic hypocotyl 1) gene encodes an essential component acting very early in the signal-transduction chain for phototropism. Arabidopsis NPH1 contains a serine-threonine kinase domain and LOV1 and LOV2 repeats that share similarity (36 to 56 percent) with Halobacterium salinarium Bat, Azotobacter vinelandii NIFL, Neurospora crassa White Collar-1, Escherichia coli Aer, and the Eag family of potassium-channel proteins from Drosophila and mammals. Sequence similarity with a known (NIFL) and a suspected (Aer) flavoprotein suggests that NPH1 LOV1 and LOV2 may be flavin-binding domains that regulate kinase activity in response to blue light-induced redox changes.
View details for Web of Science ID A1997YM23500052
View details for PubMedID 9405347
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The role of mutants in the search for the photoreceptor for phototropism in higher plants
PLANT CELL AND ENVIRONMENT
1997; 20 (6): 768-772
Abstract
Early attempts to identify the chromophore of the photoreceptor for phototropism are reviewed. Carotenoids and flavins were the principal candidates, but studies with grass coleoptiles devoid of carotenoids suggest that at least in these organs carotenoids are most unlikely to play that role. The status of characterization of a gene for a putative photoreceptor protein is also reviewed. As the action spectrum for phototropism resembles the absorption spectrum of a flavoprotein, flavoproteins are attractive candidates at present, especially since the CRY1 photoreceptor in Arabidopsis thaliana that mediates blue light-dependent hypocotyl growth suppression has flavin adenine dinucleotide as one of its two chromophores. As the second chromophore appears to be pterin, pterins should not be ruled out as candidate chromophores for the photoreceptor for phototropism.
View details for Web of Science ID A1997XG77300019
View details for PubMedID 11542766
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Mutations of Arabidopsis in potential transduction and response components of the phototropic signaling pathway
PLANT PHYSIOLOGY
1996; 112 (1): 291-296
Abstract
Four genetic loci were recently identified by mutations that affect phototropism in Arabidopsis thaliana (L.) Heyhn. seedlings. It was hypothesized that one of these loci, NPH1, encodes the apoprotein for a phototropic photoreceptor. All of the alleles at the other three mutant loci (nph2, nph3, and nph4) contained wild-type levels of the putative NPH1 protein and exhibited normal blue-light-dependent phosphorylation of the NPH1 protein. This indicated that the NPH2, NPH3, and NPH4 proteins likely function downstream of NPH1 photoactivation. We show here that, although the nph2, nph3, and nph4 mutants are all altered with respect to their phototropic responses, only the nph4 mutants are also altered in their gravitropic responsiveness. Thus, NPH2 and NPH3 appear to act as signal carriers in a phototropism-specific pathway, whereas NPH4 is required for both phototropism and gravitropism and thus may function directly in the differential growth response. Despite their altered phototropic responses in blue and green light as etiolated seedlings, the nph2 and nph4 mutants exhibited less dramatic mutant phenotypes as de-etiolated seedlings and when etiolated seedlings were irradiated with unilateral ultraviolet-A (UV-A) light. Examination of the phototropic responses of a mutant deficient in biologically active phytochromes, hy1-100, indicated that phytochrome transformation by UV-A light mediates an increase in phototropic responsiveness, accounting for the greater phototropic curvature of the nph2 and nph4 mutants to UV-A light than to blue light.
View details for Web of Science ID A1996VJ09300034
View details for PubMedID 8819327
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Evidence that zeaxanthin is not the photoreceptor for phototropism in maize coleoptiles
PLANT PHYSIOLOGY
1996; 110 (4): 1323-1328
Abstract
The photoreceptor that mediates blue-light-induced phototropism in dark-grown seedlings of higher plants has not been identified, although the carotenoid zeaxanthin has recently been proposed as the putative chromophore. In the experiments described in this paper, we analyzed phototropism and a blue-light-induced protein phosphorylation that has been genetically and physiologically implicated in phototropism in wild-type maize (Zea mays L.) seedlings and compared the results with those from seedlings that are either carotenoid deficient through a genetic lesion or have been chemically treated to block carotenoid biosynthesis. The blue-light-dependent phototropism and phosphorylation responses of seedlings deficient in carotenoids are the same as those of seedlings containing normal levels of carotenoids. These results and those in the literature make it unlikely that zeaxanthin or any other carotenoid is the chromophore of the blue-light photoreceptor for phototropism or the blue-light-induced phosphorylation related to phototropism.
View details for Web of Science ID A1996UF33400033
View details for PubMedID 11536774
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Light and the genesis of form in plants
18th Annual Riverside Symposium in Plant Physiology - Regulation of Plant Growth and Development By Light
AMER SOC PLANT PHYSIOLOGISTS. 1996: 1–8
View details for Web of Science ID A1996BG20A00001
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Photomorphogenic systems
NATO Advanced Study Institute on Light as Energy Source and Information Carrier in Plant Photophysiology
PLENUM PRESS DIV PLENUM PUBLISHING CORP. 1996: 159–167
View details for Web of Science ID A1996BF84B00013
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BLUE-LIGHT PERCEPTION BY ENDOGENOUS REDOX COMPONENTS OF THE PLANT PLASMA-MEMBRANE
PHOTOCHEMISTRY AND PHOTOBIOLOGY
1995; 61 (5): 518-522
View details for Web of Science ID A1995QZ34600016
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MUTATIONS IN THE NPH1 LOCUS OF ARABIDOPSIS DISRUPT THE PERCEPTION OF PHOTOTROPIC STIMULI
PLANT CELL
1995; 7 (4): 473-485
Abstract
The phototropic response is an important component of seedling establishment in higher plants because it orients the young seedlings for maximal photosynthetic light capture. Despite their obvious importance, little is known about the mechanisms underlying the perception and transduction of the light signals that induce phototropic curvatures. Here, we report the isolation of eight mutants of Arabidopsis that lack or have severely impaired phototropic responses. These nph (for nonphototropic hypocotyl) mutants comprise four genetic loci: nph1, nph2, nph3, and nph4. Physiological and biochemical characterization of the nph1 allele series indicated that the NPH1 locus may encode the apoprotein for a dual-chromophoric or multichromophoric holoprotein photoreceptor capable of absorbing UV-A, blue, and green light and that this photoreceptor regulates all the phototropic responses of Arabidopsis. It appears that the NPH1 protein is most likely a 120-kD plasma membrane-associated phosphoprotein because all of the nph1 mutations negatively affected the abundance of this protein. In addition, the putative NPH1 photoreceptor protein is genetically and biochemically distinct from the HY4 protein, which most likely acts as a photoreceptor for blue light-mediated hypocotyl growth inhibition. Furthermore, the NPH1 and HY4 proteins are not functionally redundant because mutations in either gene alone affect only one physiological response but not the other, thus providing strong support for the hypothesis that more than one blue light photoreceptor is required for the normal growth and development of a seedling.
View details for Web of Science ID A1995QV89400009
View details for PubMedID 7773019
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INVOLVEMENT OF THIOL-GROUPS IN BLUE-LIGHT-INDUCED PHOSPHORYLATION OF A PLASMA MEMBRANE-ASSOCIATED PROTEIN FROM COLEOPTILE TIPS OF ZEA-MAYS L
ZEITSCHRIFT FUR NATURFORSCHUNG SECTION C-A JOURNAL OF BIOSCIENCES
1995; 50 (3-4): 231-234
Abstract
Light-induced phosphorylation of a 114 kDa protein in plasma membranes isolated from the tips of maize coleoptiles was investigated in the presence of several thiol reagents at the concentration of 1 mM. Dark phosphorylation of the protein was not affected but light-induced phosphorylation was inhibited 50% with iodoacetamide, 75% with N-ethylmaleimide and 93% with N-phenylmaleimide. Previous incubation of the inhibitors with mercaptoethanol abolished the inhibitory activity completely. N-phenyl-maleimide showed the same inhibition whether it was applied before or after irradiation of the sample. Involvement of thiol group(s) in processes after photoexcitation is discussed.
View details for Web of Science ID A1995QU93100012
View details for PubMedID 7766258
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INDIVIDUAL MEMBERS OF THE CAB GENE FAMILY DIFFER WIDELY IN FLUENCE RESPONSE
PLANT PHYSIOLOGY
1995; 107 (1): 161-165
View details for Web of Science ID A1995QB24700019
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BLUE-LIGHT INDUCES PHOSPHORYLATION AT SERYL RESIDUES ON A PEA (PISUM-SATIVUM L) PLASMA-MEMBRANE PROTEIN
PLANT PHYSIOLOGY
1994; 104 (4): 1317-1324
View details for Web of Science ID A1994NF61500028
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THE TRANSDUCTION OF BLUE-LIGHT SIGNALS IN HIGHER-PLANTS
ANNUAL REVIEW OF PLANT PHYSIOLOGY AND PLANT MOLECULAR BIOLOGY
1994; 45: 143-171
View details for Web of Science ID A1994NU95900007
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PLANT BIOLOGY - NEW LIGHT ON STEM GROWTH
NATURE
1993; 366 (6451): 110-111
View details for Web of Science ID A1993MG21600028
View details for PubMedID 8232548
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CORRELATION OF BLUE LIGHT-INDUCED PHOSPHORYLATION TO PHOTOTROPISM IN ZEA-MAYS L
PLANT PHYSIOLOGY
1993; 102 (4): 1219-1225
View details for Web of Science ID A1993LR96900019
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BLUE LIGHT-INDUCED PHOSPHORYLATION OF A PLASMA MEMBRANE-ASSOCIATED PROTEIN IN ZEA-MAYS L
PLANT PHYSIOLOGY
1993; 102 (4): 1211-1218
Abstract
Blue light induces a variety of photomorphogenic responses in higher plants, among them phototropic curvature, the bending of seedlings toward a unidirectional light source. In dark-grown coleoptiles of maize (Zea mays L.) seedlings, blue light induces rapid phosphorylation of a 114-kD protein at fluence levels that are sufficient to stimulate phototropic curvature. Phosphorylation in response to blue light can be detected in vivo in coleoptile tips preincubated in 32Pi or in vitro in isolated membranes supplemented with [[gamma]-32P]ATP. Phosphorylation reaches a maximum level in vitro within 2 min following an inductive light pulse, but substantial labeling occurs within the first 15 s. Isolated membranes remain activated for several minutes following an in vitro blue light stimulus, even in the absence of exogenous ATP. Phosphoamino acid analysis of the 114-kD protein detected phosphoserine and a trace of phosphothreonine. The kinase involved in phosphorylating the protein in vitro is not dependent on calcium. The 114-kD protein itself has an apparent binding site for ATP, detected by incubating with the nonhydrolyzable analog, 5[prime]-p-fluorosulfonyl-benzoyladenosine. This result suggests that the 114-kD protein, which becomes phosphorylated in response to blue light, may also be capable of kinase activity.
View details for Web of Science ID A1993LR96900018
View details for PubMedCentralID PMC158907
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A PEA PLASMA-MEMBRANE PROTEIN EXHIBITING BLUE LIGHT-INDUCED PHOSPHORYLATION RETAINS PHOTOSENSITIVITY FOLLOWING TRITON SOLUBILIZATION
PLANT PHYSIOLOGY
1993; 101 (2): 647-655
View details for Web of Science ID A1993KM09400040
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BLUE LIGHT-INDUCED PHOSPHORYLATION OF A PLASMA-MEMBRANE PROTEIN IN PEA - A STEP IN THE SIGNAL-TRANSDUCTION CHAIN FOR PHOTOTROPISM
AUSTRALIAN JOURNAL OF PLANT PHYSIOLOGY
1993; 20 (4-5): 393-403
View details for Web of Science ID A1993MC82100003
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BLUE-LIGHT ACTIVATES A SPECIFIC PROTEIN-KINASE IN HIGHER-PLANTS
PLANT PHYSIOLOGY
1992; 100 (2): 655-661
Abstract
Blue light mediates the phosphorylation of a membrane protein in seedlings from several plant species. When crude microsomal membrane proteins from dark-grown pea (Pisum sativum L.), sunflower (Helianthus annuus L.), zucchini (Cucurbita pepo L.), Arabidopsis (Arabidopsis thaliana L.), or tomato (Lycopersicon esculentum L.) stem segments, or from maize (Zea mays L.), barley (Hordeum vulgare L.), oat (Avena sativa L.), wheat (Triticum aestivum L.), or sorghum (Sorghum bicolor L.) coleoptiles are illuminated and incubated in vitro with [gamma-(32)P]ATP, a protein of apparent molecular mass from 114 to 130 kD is rapidly phosphorylated. Hence, this system is probably ubiquitous in higher plants. Solubilized maize membranes exposed to blue light and added to unirradiated solubilized maize membranes show a higher level of phosphorylation of the light-affected protein than irradiated membrane proteins alone, suggesting that an unirradiated substrate is phosphorylated by a light-activated kinase. This finding is further demonstrated with membrane proteins from two different species, where the phosphorylated proteins are of different sizes and, hence, unambiguously distinguishable on gel electrophoresis. When solubilized membrane proteins from one species are irradiated and added to unirradiated membrane proteins from another species, the unirradiated protein becomes phosphorylated. These experiments indicate that the irradiated fraction can store the light signal for subsequent phosphorylation in the dark. They also support the hypothesis that light activates a specific kinase and that the systems share a close functional homology among different higher plants.
View details for Web of Science ID A1992JT86000018
View details for PubMedID 16653043
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WHAT REMAINS OF THE CHOLODNY-WENT THEORY - ITS ALIVE AND WELL IN MAIZE
PLANT CELL AND ENVIRONMENT
1992; 15 (7): 763-763
View details for Web of Science ID A1992JN64400003
View details for PubMedID 11541802
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ETHYLENE IS NOT INVOLVED IN THE BLUE LIGHT-INDUCED GROWTH-INHIBITION OF RED LIGHT-GROWN PEAS
PLANT PHYSIOLOGY
1992; 100 (1): 95-99
Abstract
Although the growth of intact plants is inhibited by irradiation with blue light, the growth rate of isolated stem segments is largely unaffected by blue light. We hypothesized that this loss of responsiveness was a result of ethylene production as part of the wounding response. However, we found no interaction between ethylene- and blue light-induced growth inhibition in dark- or red light-grown seedlings of pea (Pisum sativum L.). Inhibition of growth begins in dark-grown seedlings exposed to blue light within 3 min of the onset of blue light, as was known for red light-grown seedlings. By contrast, ethylene-induced inhibition of growth occurs only after a lag of 20 to 30 min or more (dark-grown seedlings) or 60 min (red light-grown seedlings). Also, the inhibition response of red light-grown seedlings is the same whether ethylene is present from the onset of continuous blue-light treatment or not. Finally the spatial distribution of inhibition following blue light was different from that following ethylene treatment.
View details for Web of Science ID A1992JR21100015
View details for PubMedID 16653007
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LIGHT-INDUCED PHOSPHORYLATION OF A MEMBRANE-PROTEIN PLAYS AN EARLY ROLE IN SIGNAL TRANSDUCTION FOR PHOTOTROPISM IN ARABIDOPSIS-THALIANA
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1992; 89 (10): 4718-4721
Abstract
Blue light is known to cause rapid phosphorylation of a membrane protein in etiolated seedlings of several plant species, a protein that, at least in etiolated pea seedlings and maize coleoptiles, has been shown to be associated with the plasma membrane. The light-driven phosphorylation has been proposed on the basis of correlative evidence to be an early step in the signal transduction chain for phototropism. In the Arabidopsis thaliana mutant JK224, the sensitivity to blue light for induction of first positive phototropism is known to be 20- to 30-fold lower than in wild type, whereas second positive curvature appears to be normal. While light-induced phosphorylation can be demonstrated in crude membrane preparations from shoots of the mutant, the level of phosphorylation is dramatically lower than in wild type, as is the sensitivity to blue light. Another A. thaliana mutant, JK218, that completely lacks any phototropic responses to up to 2 h of irradiation, shows a normal level of light-induced phosphorylation at saturation. Since its gravitropic sensitivity is normal, it is presumably blocked in some step between photoreception and the confluence of the signal transduction pathways for phototropism and gravitropism. We conclude from mutant JK224 that light-induced phosphorylation plays an early role in the signal transduction chain for phototropism in higher plants.
View details for Web of Science ID A1992HU97700102
View details for PubMedID 11537679
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A PHOTORECEPTOR SYSTEM REGULATING INVIVO AND INVITRO PHOSPHORYLATION OF A PEA PLASMA-MEMBRANE PROTEIN
PHOTOCHEMISTRY AND PHOTOBIOLOGY
1992; 55 (5): 773-781
View details for Web of Science ID A1992HR92800020
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A FLAVOPROTEIN MAY MEDIATE THE BLUE LIGHT-ACTIVATED BINDING OF GUANOSINE 5'-TRIPHOSPHATE TO ISOLATED PLASMA-MEMBRANES OF PISUM-SATIVUM L
PHOTOCHEMISTRY AND PHOTOBIOLOGY
1992; 55 (4): 595-603
View details for Web of Science ID A1992HK37400017
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EFFECTS OF HIGH LIGHT STRESS ON CAROTENOID-DEFICIENT CHLOROPLASTS IN PISUM-SATIVUM
PLANT PHYSIOLOGY
1990; 94 (4): 1663-1670
Abstract
The effects of high light stress on chloroplast ultrastructure and protein and mRNA composition were investigated in carotenoid-deficient peas (Pisum sativum, L.). In low light, the thylakoid membrane polypeptide pattern was altered, with several prominent chlorophyll-binding proteins present in diminished amounts. This change was found to be reflected in the ultrastructural organization of internal chloroplast membranes. In contrast to the normal grana stacking found in the controls, carotenoid-deficient plastids contained long, unstacked lamellae. Exposure to photooxidative light that resulted in destruction of >70% of chlorophyll did not lead to changes in total RNA and total cellular protein patterns. This treatment did lead to gross alterations in the chloroplast structure. Within 24 hours the plastid was seen as a swollen vesicle with only a few membrane remnants still present. Accumulation of five plastid-encoded mRNAs encoding a diverse array of photosynthetic proteins was found to be affected in different ways. While psaA mRNA was rapidly reduced by more than 75%, levels of psbF/E and atpB/E were reduced by 50%. psbA and petA mRNAs, on the other hand, appeared to be more resistant to photobleaching and remained relatively unchanged during 24 hours of high fluence-rate light treatment.
View details for Web of Science ID A1990EN70000024
View details for PubMedID 16667900
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TRANSPORT OF INDOLE-3-ACETIC-ACID DURING GRAVITROPISM IN INTACT MAIZE COLEOPTILES
PLANT PHYSIOLOGY
1990; 94 (4): 1763-1769
Abstract
We have investigated the transport of tritiated indole-3-acetic acid (IAA) in intact, red light-grown maize (Zea mays) coleoptiles during gravitropic induction and the subsequent development of curvature. This auxin is transported down the length of gravistimulated coleoptiles at a rate comparable to that in normal, upright plants. Transport is initially symmetrical across the coleoptile, but between 30 and 40 minutes after plants are turned horizontal a lateral redistribution of the IAA already present in the transport stream occurs. By 60 minutes after the beginning of the gravitropic stimulus, the ratio of tritiated tracer auxin in the lower half with respect to the upper half is approximately 2:1. The redistribution of growth that causes gravitropic curvature follows the IAA redistribution by 5 or 10 minutes at the minimum in most regions of the coleoptile. Immobilization of tracer auxin from the transport stream during gravitropism was not detectable in the most apical 10 millimeters. Previous reports have shown that in intact, red light-grown maize coleoptiles, endogenous auxin is limiting for growth, the tissue is linearly responsive to linearly increasing concentrations of small amounts of added auxin, and the lag time for the stimulation of straight growth by added IAA is approximately 8 or 9 minutes (TI Baskin, M Iino, PB Green, WR Briggs [1985] Plant Cell Environ 8: 595-603; TI Baskin, WR Briggs, M Iino [1986] Plant Physiol 81: 306-309). We conclude that redistribution of IAA in the transport stream occurs in maize coleoptiles during gravitropism, and is sufficient in degree and timing to be the immediate cause of gravitropic curvature.
View details for Web of Science ID A1990EN70000039
View details for PubMedID 16667914
View details for PubMedCentralID PMC1077450
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TRANSPORT OF INDOLEACETIC-ACID IN INTACT CORN COLEOPTILES
PLANT PHYSIOLOGY
1990; 94 (2): 417-423
Abstract
We have characterized the transport of [(3)H]indoleacetic acid (IAA) in intact corn (Zea mays L.) coleoptiles. We have used a wide range of concentrations of added IAA (28 femtomoles to 100 picomoles taken up over 60 minutes). The shape of the transport curve varies with the concentration of added IAA, although the rate of movement of the observed front of tracer is invariant with concentration. At the lowest concentration of tracer used, the labeled IAA in the transport stream is not detectably metabolized or immobilized, curvature does not develop as a result of tracer application, and normal phototropic and gravitropic responsiveness are not affected. Therefore we believe we are observing the transport of true tracer quantities of labeled auxin at this lowest concentration.
View details for Web of Science ID A1990EF74800006
View details for PubMedID 16667729
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ACTION DICHROISM IN PERCEPTION OF VECTORIAL PHOTOEXCITATION IN THE SOLAR-TRACKING LEAF OF LAVATERA-CRETICA L
PLANTA
1990; 181 (2): 184-190
View details for Web of Science ID A1990DC57800005
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SOME SPECTRAL PROPERTIES OF SEVERAL SOIL TYPES - IMPLICATIONS FOR PHOTOMORPHOGENESIS
PLANT CELL AND ENVIRONMENT
1990; 13 (3): 287-294
View details for Web of Science ID A1990DE02900010
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ENHANCED DIAPHOTOTROPIC RESPONSE TO VECTORIAL EXCITATION IN SOLAR-TRACKING LEAVES OF LAVATERA-CRETICA BY AN IMMEDIATELY PRECEDING OPPOSITE VECTORIAL EXCITATION
JOURNAL OF PLANT PHYSIOLOGY
1990; 135 (5): 601-607
View details for Web of Science ID A1990CP31200019
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CHARACTERIZATION OF A RAPID, BLUE LIGHT-MEDIATED CHANGE IN DETECTABLE PHOSPHORYLATION OF A PLASMA-MEMBRANE PROTEIN FROM ETIOLATED PEA (PISUM-SATIVUM-L) SEEDLINGS
PLANT PHYSIOLOGY
1990; 92 (1): 179-185
Abstract
When crude microsomal membranes from apical stem segments of etiolated Pisum sativum L. cv Alaska are mixed in vitro with gamma-[(32)P]ATP, a phosphorylated band of apparent molecular mass 120 kilodaltons can be detected on autoradiographs of sodium dodecyl sulfate electrophoresis gels. If the stem sections are exposed to blue light immediately prior to membrane isolation, this band is not evident. The response is observed most strongly in membranes from the growing region of the stem, but no 120 kilodalton radiolabeled band is detected in membranes from the developing buds. Fluence-response curves for the reaction show that the system responds to blue light above about 0.3 micromole per square meter, and the visible phosphorylation completely disappears above 200 micromoles per square meter. Reciprocity is valid for the system, because varying illumination time or fluence rate give similar results. If the stem segments are left in the dark following a saturating blue irradiation, the radio-labeled band begins to return after about 10 minutes and is as intense as that from the dark controls within 45 to 60 minutes. A protein that comigrates with the phosphorylated protein on polyacrylamide gels is also undetectable after saturating blue light irradiations. The fluence range in which the protein band disappears is the same as that for the disappearance of the phosphorylation band. Its dark recovery kinetics and tissue distribution also parallel those for the phosphorylation. In vitro irradiation of the isolated membranes also results in a phosphorylation change at that molecular mass, but in the opposite direction. Comparisons of the kinetics, tissue distribution, and dark recovery of the phosphorylation response with those published for blue light-mediated phototropism or rapid growth inhibition indicate that the phosphorylation could be linked to one or both of those reactions. However, the fluence-response relationships for the change in detectable phosphorylation match quite closely those reported for phototropism but not those for growth inhibition. Blue light has also been found to regulate the capacity for in vitro phosphorylation of a second protein. It has an apparent molecular mass of 84 kilodaltons and is localized primarily in basal stem sections.
View details for Web of Science ID A1990CJ20600029
View details for PubMedID 16667244
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EVIDENCE FOR A PHYTOCHROME-MEDIATED PHOTOTROPISM IN ETIOLATED PEA-SEEDLINGS
PLANT PHYSIOLOGY
1989; 89 (2): 493-497
Abstract
Entirely etiolated pea seedlings (Pisum sativum, L. cv Alaska) were tested for a phototropic response to short pulses of unilateral blue light. They responded with small curvatures resembling in fluence-dependence and kinetics of development a phytochrome-mediated phototropic response previously described in maize mesocotyls. Irradiations from above with saturating red or far-red light, either immediately before or after the unilateral phototropic stimulus, strongly reduced or eliminated subsequent positive phototropic curvature. Only blue light from above, however, entirely eliminated curvature at all fluences of stimulus. It is concluded that the phototropism is primarily a result of phytochrome action.
View details for Web of Science ID A1989T386400019
View details for PubMedID 16666571
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REGULATION OF PEA EPICOTYL ELONGATION BY BLUE-LIGHT - FLUENCE-RESPONSE RELATIONSHIPS AND GROWTH DISTRIBUTION
PLANT PHYSIOLOGY
1989; 89 (1): 293-298
Abstract
Irradiation with blue light causes a rapid decrease in stem elongation in Pisum sativum. Growing plants under continuous red light allowed us to study the fluence dependence and spatial distribution of blue-induced growth effects without interference from large changes in the ratio of the far-red absorbing form of phytochrome to total phytochrome. The magnitude of the inhibition generated by a 30-second pulse of blue light was linearly related to the log of the fluence applied over two orders of magnitude. Reciprocity held for irradiations with a pulse length shorter than the lag time for the response. The spatial distribution of inhibition was studied by marking the growing zone and photographing the stem at 10-minute intervals before, during, and after a 1-hour exposure to blue light. The region just below the hook does not undergo any perceptible change in growth rate while growth is nearly 100% inhibited in the base of the third internode.
View details for Web of Science ID A1989R776600047
View details for PubMedID 16666529
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NUCLEAR-CYTOPLASMIC PARTITIONING OF PHYTOCHROME-REGULATED TRANSCRIPTS IN PISUM-SATIVUM
PLANT PHYSIOLOGY
1988; 88 (4): 1397-1402
Abstract
Nuclear and cytoplasmic mRNAs for several phytochrome-regulated genes were examined in Pisum seedlings in order to investigate possible light effects on mRNA partitioning between the nucleus and cytoplasm. Transcripts from each of five light-regulated genes exhibited different responses to a variety of light treatments, but for each transcript we observed a characteristic linear relationship between nuclear and cytoplasmic levels over a wide range of total transcript abundance. Different mRNAs are characterized by different nuclear-cytoplasmic ;partitioning coefficients', indicating that post-transcriptional events play a significant role in regulating the accumulation of these mRNAs during light induction.
View details for Web of Science ID A1988R574400079
View details for PubMedID 16666472
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LIGHT-MEDIATED CHANGES IN 2 PROTEINS FOUND ASSOCIATED WITH PLASMA-MEMBRANE FRACTIONS FROM PEA STEM SECTIONS
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1988; 85 (21): 8003-8007
Abstract
Irradiation of etiolated pea (Pisum sativum L.) seedlings with white light affects two proteins, both of monomer molecular mass near 120 kDa. Both proteins have been detected in association with plasma membrane fractions. The first is identifiable in that it becomes heavily phosphorylated when the membranes are incubated with exogenous ATP. The second of these proteins is phytochrome, as determined by electrophoretic transfer (Western) blot analysis. Measurable phosphorylation and phytochrome (the latter detected by antigenicity) decline when the tissue is irradiated with white light prior to membrane isolation and in vitro phosphorylation. The phosphorylated protein is probably not phytochrome for three reasons. (i) It shows a slightly different distribution in sucrose gradients. (ii) Red light causes a gradual decline in the phytochrome that is associated with membrane fractions but has a negligible effect on the phosphorylatable protein; blue light, on the other hand, causes significantly slower loss of phytochrome than does red light but brings about a rapid decline in the phosphorylation signal. (iii) The molecular masses are not identical. The association of both proteins with membrane fractions is probably neither ionic nor, at least for the phosphorylatable protein, the consequence of entrapment of soluble proteins in vesicles formed during tissue extraction. Phytochrome is lost from the membrane fractions during irradiation, as judged by loss of antigenicity. Whether the phosphorylatable protein is lost, a specific kinase is lost, phosphatase activity increases, or phosphorylatable sites are blocked as a consequence of blue light treatment is not known.
View details for Web of Science ID A1988Q834100037
View details for PubMedID 16593988
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LIGHT EFFECTS ON SEVERAL CHLOROPLAST COMPONENTS IN NORFLURAZON-TREATED PEA-SEEDLINGS
PLANT PHYSIOLOGY
1988; 88 (2): 340-347
Abstract
Changes occurring in several chloroplast components during Norflurazon-induced photobleaching of Pisum sativum seedlings were investigated. mRNA steady state levels of the chlorophyll a/b-binding protein of photosystem II, ferredoxin I, the small and large subunits of ribulose 1,5-bisphosphate carboxylase, and pEA214 and pEA207, two other light-responsive genes, were determined during chlorophyll photooxidation. Relative transcription rates were assayed in isolated nuclei. The results illustrate a complex set of interactions regulating expression of the nuclear and chloroplast genomes. Photobleaching was found to affect the expression of the various genes in different ways. While transcript levels of the chlorophyll a/b-binding protein decreased by more than 80% under photooxidative light conditions in carotenoid-deficient peas, levels of ferredoxin, the small and large subunits of ribulose 1,5-bisphosphate carboxylase, and pEA214 mRNAs were reduced by less than 50%. pEA207 mRNA levels, on the other hand, were resistant to the effects of photobleaching. Analyses of chlorophylls a and b and the chlorophyll a/b-binding protein suggest that accumulation of the protein and its mRNA are coordinated with chlorophyll abundance at several steps. In addition to post-transcriptional regulation at the level of mRNA and protein stability, there may exist coordination at the transcriptional stage.
View details for Web of Science ID A1988Q571600020
View details for PubMedID 16666305
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PHOTOTROPISM IN HIGHER-PLANTS - CONTROVERSIES AND CAVEATS
BOTANICA ACTA
1988; 101 (2): 133-139
View details for Web of Science ID A1988Q547700009
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PHYTOCHROME REGULATION OF GREENING IN BARLEY - EFFECTS ON CHLOROPHYLL ACCUMULATION
PLANT PHYSIOLOGY
1988; 86 (2): 435-440
Abstract
Red light treatment of dark-grown 6-day-old barley seedlings (Hordeum vulgare L.) strongly reduces the lag in chlorophyll accumulation in subsequent white light over that found in dark control seedlings placed under white light. Fluence-response studies show that the effect has both very low fluence and low fluence components. Kinetic studies indicate that the reduction in lag begins immediately following either a low fluence or a very low fluence red irradiation, with the initial rate of change significantly lower after the very low fluence treatment and showing sharp far red-absorbing form of phytochrome dependence. In both cases, the effect is maximal after roughly 4 hours, either remaining fairly constant (very low fluence) or declining somewhat (low fluence) thereafter. Saturating far red light alone yields a response equivalent to very low fluence red, and will reverse only the low fluence component of the red response. Escape from far red reversibility occurs gradually over about a 3 hour period. Since the kinetics described here differ from those in the literature related to phytochrome effects on transcription of the mRNA for the light-harvesting chlorophyll a/b-binding protein, we conclude that the phytochrome-regulated component of chlorophyll accumulation is not limited by transcription of the mRNA for its major apoprotein. Leaf segments vacuum-infiltrated with water retain the capacity to green in white light. If they are infiltrated with mannitol solutions of various concentrations, their capacity to green declines sharply at concentrations above 0.2 molar. These results bear on interpretation of run-on transcription experiments with isolated nuclei: preparation of the nuclei involves enzymic digestion of the tissue in the presence of 0.7 molar mannitol for 2.5 hours, to obtain protoplasts prior to breaking the cells. The results here make it unlikely that normal transcriptional regulation is occurring during this procedure.
View details for Web of Science ID A1988M249600026
View details for PubMedID 16665926
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INTERACTION BETWEEN CORTICAL CYLINDER AND EPIDERMIS DURING AUXIN-MEDIATED GROWTH IN PEA INTERNODES
PLANT SCIENCE
1988; 54 (1): 23-28
View details for Web of Science ID A1988M629400003
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PHYTOCHROME REGULATION OF GREENING IN PISUM - CHLOROPHYLL ACCUMULATION AND ABUNDANCE OF MESSENGER-RNA FOR THE LIGHT-HARVESTING CHLOROPHYLL A/B BINDING-PROTEINS
PLANT PHYSIOLOGY
1988; 86 (1): 299-305
Abstract
A brief pulse of red light eliminates or reduces the lag in chlorophyll accumulation that occurs when dark-grown pea seedlings are transferred to continuous white light. The red light pulse also induces the accumulation of specific mRNAs. We compared time courses, escape from reversal by far-red light, and fluence-response behavior for induction of mRNA for the light-harvesting chlorophyll a/b binding proteins (Cab mRNA) with those for induction of rapid chlorophyll accumulation in seedlings of Pisum sativum cv Alaska. In both cases the time courses of low fluence and very low fluence responses diverged from each other in a similar fashion: the low fluence responses continued to increase for at least 24 hours, while the very low fluence responses reached saturation by 8 to 16 hours. Both responses escaped from reversibility by far-red slowly, approaching the red control level after 16 hours. The fluence-response curve for the Cab mRNA increase, on the other hand, showed threshold and saturation at fluences 10-fold lower than threshold and saturation values for the greening response. Therefore, the level of Cab mRNA, as measured by the presence of sequences hybridizing to a cDNA probe, does not limit the rate of chlorophyll accumulation after transfer of pea seedlings to white light. The Cab mRNA level in the buds of seedlings grown under continuous red light remained high even when the red fluence rate was too low to allow significant greening. In this case also, abundance of Cab mRNA cannot be what limits chlorophyll accumulation.
View details for Web of Science ID A1988L852100058
View details for PubMedID 16665885
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GROWTH, INVIVO EXTENSIBILITY, AND TISSUE TENSION IN DEVELOPING PEA INTERNODES
PLANT PHYSIOLOGY
1988; 86 (1): 306-311
Abstract
The relationship between growth, in vivo extensibility, and tissue tension in the first 3 internodes of 5, 6, and 7 day-old pea plants (Pisum sativum L. cv Alaska), grown under continuous red light was investigated. The upper 15 millimeters of each internode was marked with ink and its elongation growth measured over the next subsequent 8 hours. In vivo extensibility was measured by stretching living tissue at constant force (creep test) in a custom-built extensiometer. Tissue tension was determined by (a) measuring the rate of expansion of the isolated cortical cylinder after adding water and the amount of contraction of the epidermis after peeling, and (b) by use of the ;split section test.' A good correlation between rate of elongation growth, in vivo extensibility, and tissue tension was established. The epidermis peeled from the growing third internode of 7 day-old plants and measured immediately showed a plastic extensibility (E(pl) twice that of peels from nongrowing excised sections. This high E(pl)-value was lost on incubation of the sections in distilled water, and was subsequently restored by incubating the sections in auxin (indole-3-acetic acid). We conclude that the in situ growth of the internodes is a function of tissue-tension, which provides the driving force of organ growth, and the extensibility (E(pl) of the outer epidermal wall, which is in the growing plant in a ;loosened' state. We furthermore suggest that in the intact plant auxin is causally involved in the wall loosening process in the epidermis.
View details for Web of Science ID A1988L852100059
View details for PubMedID 16665886
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DIFFERENTIAL EFFECT OF AUXIN ON INVIVO EXTENSIBILITY OF CORTICAL CYLINDER AND EPIDERMIS IN PEA INTERNODES
PLANT PHYSIOLOGY
1987; 84 (4): 1361-1366
Abstract
The effect of auxin indole-3-acetic acid (IAA) on growth and in vivo extensibility of third internode sections from red light grown pea seedlings (Pisum sativum L. cv Alaska) and the isolated tissues (cortex plus vascular tissue = cortical cylinder, and epidermis) was investigated. Living tissue was stretched at constant force (creep test) in a custom-built extensiometer. In the intact section, IAA-induced increase in total (E(tot)), elastic (E(el)), and plastic (E(pl)) extensibility is closely related to the growth rate. The extensibility of the cortical cylinder, measured immediately after peeling of intact sections incubated for 4 hours in IAA, is not increased by IAA. Epidermal strips, peeled from growing sections incubated in IAA, show a E(pl) increase, which is correlated to the growth rate of the intact segments. The isolated cortical cylinder expands in water; IAA has only a small growth-promoting effect. The extensibility of the cortical cylinder is not increased by IAA. Epidermal strips contract about 10% on isolation. When incubated in IAA, they do not elongate, but respond with an E(pl) increase. The amount of expansion of the cortical cylinder and contraction of the epidermis (tissue tension), measured immediately following excision and peeling, stays constant during IAA-induced growth of intact sections. The results support the hypothesis that IAA induces growth of the intact section by causing an E(pl) increase of the outer epidermal wall. The driving force comes from the expansion of the cortical cylinder which is under constant compression in the intact section.
View details for Web of Science ID A1987J769100073
View details for PubMedID 16665611
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SPECIFIC MESSENGER-RNA AND RIBOSOMAL-RNA LEVELS IN GREENING PEA LEAVES DURING RECOVERY FROM IRON STRESS
PLANT PHYSIOLOGY
1987; 84 (2): 409-414
Abstract
Hydroponically grown pea seedlings (Pisum sativum L., cv Alaska) were subjected to Fe stress for 10 to 16 days to produce mature chlorotic leaves. Greening was initiated by adding Fe to the nutrient solution. The levels of chlorophylls, chloroplast, and cytoplasmic rRNAs, and specific chloroplast- and nucleus-encoded mRNAs were all significantly lower in leaves developing during iron stress than in nonstressed leaves. In plants greening after addition of Fe, nuclear transcripts encoding chlorophyll a/b-binding protein and the small subunit of ribulose bisphosphate carboxylase/oxygenase increased about 5-fold in abundance following an 18 to 24 hour lag, as did the chloroplast-encoded transcript for the large subunit of the carboxylase/oxygenase. Chloroplast rRNA showed an increase over that in continually stressed control leaves only after a 40 hour lag. The chloroplast-encoded transcript encoding the Q(B)-binding 32 kilodalton polypeptide of Photosystem II showed little change during greening. Chlorophyll itself increased gradually after a lag period of 24 hours, with an increase in chlorophyll a slightly preceding that of chlorophyll b. Kinetic considerations suggest that the changes observed represent a coordinate series of events initiated by readdition of Fe and occurring in parallel. Though accumulation of mRNA for light-harvesting, chlorophyll-a/b-binding protein might limit chlorophyll accumulation at the onset, subsequent changes in the mRNA do not parallel chlorophyll changes. All three of the mRNAs showing recovery on addition of Fe to Fe-stressed plants undergo sharp diurnal fluctuations in abundance. Such fluctuations are comparable to those in nonstressed controls (mRNA for light-harvesting protein) or considerably more pronounced (mRNAs for carboxylase large and small subunits). The carboxylase small subunit mRNA and that for light-harvesting chlorophyll-binding protein were measured under constant conditions of light and temperature. Though a rhythm in greening leaves was hard to detect, it was prominent in the Fe-sufficient controls, persisting undamped through three full cycles for both mRNAs, and hence is probably circadian.
View details for Web of Science ID A1987H938400039
View details for PubMedID 16665453
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RAPID AUXIN-INDUCED STIMULATION OF CELL-WALL SYNTHESIS IN PEA INTERNODES
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1987; 84 (9): 2747-2751
Abstract
The effect of auxin (indole-3-acetic acid; IAA) on growth and incorporation of myo-[2-(3)H(N)]inositol ([(3)H]Ins) into noncellulosic polysaccharides in the cell walls of third internode sections from red light-grown pea seedlings (Pisum sativum L. cv. Alaska) was investigated. Intact sections were incubated on [(3)H]Ins for 4 hr to permit uptake of the tracer and then IAA was added. Growth started after a lag phase of 15 min under these conditions. The sections were removed from the tracer and separated into epidermis and cortical cylinder (cortex plus vascular tissue). In the epidermis, IAA-induced stimulation of [(3)H]Ins incorporation started after a lag of 15 min. The amount of incorporation was 15% higher after 30 min and 24% higher after 2 hr than in the control. In the cortical cylinder, IAA-induced stimulation of [(3)H]Ins incorporation started only approximately 1 hr after adding IAA. The ionophore monensin (20 muM) inhibited the IAA-induced growth by 95%. Under these conditions, the IAA-induced stimulation of [(3)H]Ins incorporation and the IAA-induced increase in in vivo extensibility of the sections was almost completely inhibited, although oxygen uptake was unaffected. We suggest that wall synthesis (as represented by [(3)H]Ins incorporation) and wall loosening (increase in in vivo extensibility) are related processes. The results support the hypothesis that IAA induces growth by rapid stimulation of cell wall synthesis in the growth-limiting epidermal cell layer.
View details for Web of Science ID A1987H173100038
View details for PubMedID 16593829
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CHLOROPLAST MOVEMENT AND LIGHT TRANSMISSION IN ULVA - THE SIEVE EFFECT IN A LIGHT-SCATTERING SYSTEM
ACTA PHYSIOLOGIAE PLANTARUM
1987; 9 (3): 149-162
View details for Web of Science ID A1987M721200004
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PHOTOMORPHOGENESIS FROM SIGNAL PERCEPTION TO GENE-EXPRESSION
PHOTOBIOCHEMISTRY AND PHOTOBIOPHYSICS
1986; 12 (3-4): 305-320
View details for Web of Science ID A1986F194700013
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PHYTOCHROME CONTROL OF SPECIFIC MESSENGER-RNA LEVELS IN DEVELOPING PEA BUDS - KINETICS OF ACCUMULATION, RECIPROCITY, AND ESCAPE KINETICS OF THE LOW FLUENCE RESPONSE
PLANT PHYSIOLOGY
1986; 81 (4): 1033-1038
Abstract
We have examined the time course for accumulation of each of 12 different nuclear gene transcripts in pea buds after irradiating dark grown seedlings with a single pulse low fluence red light (10(3) micromoles per square meter delivered in 100 seconds). The 12 time courses can be grouped into four general classes. Six transcripts (including RNAs coding for the chlorophyll a/b binding protein and ribulose-1,5-bisphosphate carboxylase) accumulate at a linear rate during 24 hours in darkness following the light pulse. Two transcripts increase rapidly at first but then reach a plateau after 3 hours and remain at that level for the next 21 hours. Another two transcripts exhibit a prolonged lag period before beginning to accumulate, and do not reach significant accumulation rates until 12 to 16 hours after the red light pulse. One transcript appears to undergo a transient increase in abundance in response to red light, but this is superimposed on a background of slowly increasing abundance of this RNA in control plants. This response, unlike all the others, exhibits reciprocity failure in experiments in which the same fluence of light is given over periods ranging between 50 and 4000 seconds.We have also examined the kinetics with which each of these 12 responses escapes from phytochrome-far-red absorbing form control by attempting to reverse the induction with far-red light given at various times after the red light pulse. Again, several different patterns are apparent for the different transcripts. The time at which far red reversibility first begins to be lost, the rate at which it is lost, and the final extent of reversibility remaining after 7 hours in the dark all differ for different transcripts. In addition, we have observed that some responses retain virtually complete photoreversibility for at least 7 hours. In some cases, a comparison of the time course and escape kinetic data indicates that relatively rapid turnover of the RNA must occur. It is not clear whether or not the rate of turnover is influenced by phytochrome.
View details for Web of Science ID A1986D680800019
View details for PubMedID 16664939
View details for PubMedCentralID PMC1075481
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OPTIMIZATION OF RED LIGHT-INDUCED ELONGATION IN AVENA-COLEOPTILE SECTIONS AND PROPERTIES OF THE PHYTOCHROME-MEDIATED GROWTH-RESPONSE
PLANT CELL AND ENVIRONMENT
1986; 9 (3): 165-173
View details for Web of Science ID A1986C431200001
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THE VECTORIAL PHOTOEXCITATION IN SOLAR-TRACKING LEAVES OF LAVATERA-CRETICA (MALVACEAE)
PHOTOCHEMISTRY AND PHOTOBIOLOGY
1985; 42 (6): 717-723
View details for Web of Science ID A1985AWZ0900017
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COMPONENTS OF VECTORIAL PHOTOEXCITATION IN SOLAR-TRACKING LEAVES OF LAVATERA-CRETICA (MALVACEAE)
PHYSIOLOGIE VEGETALE
1985; 23 (6): 913-920
View details for Web of Science ID A1985AZA3800005
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HIGH-RESOLUTION MEASUREMENT OF GROWTH DURING 1ST POSITIVE PHOTOTROPISM IN MAIZE
PLANT CELL AND ENVIRONMENT
1985; 8 (8): 595-603
View details for Web of Science ID A1985ATT6400006
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ACTIVE AUXIN UPTAKE BY ZUCCHINI MEMBRANE-VESICLES - QUANTITATION USING ELECTRON-SPIN-RESONANCE VOLUME AND DELTA-PH DETERMINATIONS
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1985; 82 (19): 6541-6545
Abstract
Closed and pH-tight membrane vesicles prepared from hypocotyls of 5-day-old dark-grown seedlings of Cucurbita pepo accumulate the plant growth hormone indole-3-acetic acid along an imposed proton gradient (pH low outside, high inside). The use of electron paramagnetic spin probes permitted quantitation both of apparent vesicle volume and magnitude of the pH gradient. Under the experimental conditions used, hormone accumulation was at minimum 20-fold, a value 4 times larger than what one would predict if accumulation reflected only diffusional equilibrium at the measured pH gradient. It is concluded that hormone uptake is an active process, with each protonated molecule of hormone accompanied by an additional proton. Experiments with ionophores confirm that it is the pH gradient itself which drives the uptake.
View details for Web of Science ID A1985ARZ4800038
View details for PubMedID 2995970
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PHYTOCHROME CONTROL OF SPECIFIC MESSENGER-RNA LEVELS IN DEVELOPING PEA BUDS - THE PRESENCE OF BOTH VERY LOW FLUENCE AND LOW FLUENCE RESPONSES
PLANT PHYSIOLOGY
1985; 78 (2): 388-393
Abstract
We have examined phytochrome regulated changes in transcript abundance for 11 different light regulated mRNAs in developing pea buds. Fluence-response curves were measured for changes in transcript abundance in response to red light pulses in both the low and very low fluence ranges. Most transcripts show only low fluence responses, with a threshold of approximately 10 micromoles per square meter. All of the low fluence responses are reversible by far red light. One transcript shows a very low fluence response, with a threshold of approximately 10(-4) micromoles per square meter. As expected, the very low fluence response is not far red reversible and in fact can be induced by far red light.Various fluences of red light were also used as pretreatments before transferring seedlings to continuous white light. One transcript responds to pretreatments in the very low fluence range, several respond to pretreatments in the low fluence range (including chlorophyll a/b binding protein RNA and ribulose-1,5-bisphosphate carboxylase RNA), and several show no response to the red light under these conditions. The threshold of these low fluence responses is approximately 10(2) micromoles per square meter, one order of magnitude greater than the threshold of the low fluence responses to red light alone.The transcripts may also be grouped by their responses to white light treatment alone. Three of the clones correspond to transcripts whose abundance decreases after a 24 hour white light treatment. The remainder of the mRNAs increase between 2- and 10-fold in response to the 24 hour white light.
View details for Web of Science ID A1985AKT7400035
View details for PubMedID 16664251
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PHYSIOLOGICAL MECHANISM OF THE AUXIN-INDUCED INCREASE IN LIGHT SENSITIVITY OF PHYTOCHROME-MEDIATED GROWTH-RESPONSES IN AVENA-COLEOPTILE SECTIONS
PLANT PHYSIOLOGY
1985; 79 (2): 349-356
Abstract
The physiology of the auxin-induced 10,000-fold increase in light sensitivity of a phytochrome-mediated growth response (Shinkle and Briggs, 1984 Proc Natl Acad Sci USA 81: 3742-3746) has been characterized in subapical coleoptile sections from dark-grown oat (Avena sativa L. cv Lodi) seedlings. Six micromolar indole-3-acetic acid (IAA) must be present for 1 hour before to 2 hour after irradiation in order to confer maximal sensitivity to light. The direct effect of IAA on growth can be separated from its effect on light sensitivity. Several classes of synthetic auxins will substitute for IAA in inducing an increase in sensitivity to light, as will both the phytotoxin fusicoccin and treatment of sections with pH 4.5 buffer. The increase in sensitivity to light induced by 6 micromolar IAA is completely inhibited by buffering the sections at pH 5.9 with 30 millimolar 2-(N-morpholino)ethanesulfonic acid. These findings suggest that the capacity to respond to very low fluences of light is regulated by extracellular pH.Between 10 and 15 millimolar K(+) will inhibit the induction of the increased sensitivity to light, independent of the mechanism of induction. The effect of K(+) appears to be specific to the process by which the sections respond to very low levels of light.
View details for Web of Science ID A1985ATH1800005
View details for PubMedID 16664413
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GROWTH DISTRIBUTION DURING 1ST POSITIVE PHOTOTROPIC CURVATURE OF MAIZE COLEOPTILES
PLANT CELL AND ENVIRONMENT
1984; 7 (2): 97-104
View details for Web of Science ID A1984SH66300004
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DIFFERENT RED-LIGHT REQUIREMENTS FOR PHYTOCHROME-INDUCED ACCUMULATION OF CAB RNA AND RBCS RNA
SCIENCE
1984; 226 (4681): 1447-1449
Abstract
For several species of plants the abundance of those transcripts encoding the chlorophyll a/b binding protein (cab RNA) and the small subunit of ribulose-1,5-biphosphate carboxylase-oxygenase (rbcS RNA) has been established as being under the control of phytochrome. However, this conclusion does not take into account the various types of phytochrome control based on both the fluence of red light necessary to induce the response and the ability of far red light either to induce or to reverse the response. The fluence of red light necessary to induce the accumulation of rbcS RNA was found to be 10,000 times greater than that necessary to induce the accumulation of cab RNA. Furthermore, far red light alone was capable of inducing the accumulation of cab RNA. It is possible, therefore, that developing pea buds accumulate cab RNA before rbcS and that cab RNA is not subject to the normal end-of-day signals affecting many phytochrome responses.
View details for Web of Science ID A1984TW06800038
View details for PubMedID 17789001
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INDOLE-3-ACETIC-ACID SENSITIZATION OF PHYTOCHROME-CONTROLLED GROWTH OF COLEOPTILE SECTIONS
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA-BIOLOGICAL SCIENCES
1984; 81 (12): 3742-3746
Abstract
Addition of 6 muM indole-3-acetic acid (IAA) to incubation buffer increases the sensitivity of coleoptile sections cut from dark-grown Avena sativa L. cv. Lodi to red light by a factor of 10,000, relative to the response in the absence of added IAA, without changing the maximum amount of light-induced growth. From 0.03 to 4 muM IAA sections show at least a 100-fold increase in sensitivity to red light relative to the response in the absence of added IAA. In this IAA concentration range, the light-induced increase in elongation shows two phases of response to red-light fluence, which are separated by a plateau. The biphasic fluence-response curve is also characteristic of the red-light-induced stimulation of coleoptile growth in intact dark-grown seedlings. The effect of IAA on the sensitivity of the phytochrome-mediated growth response appears to be on some step in the transduction of the phytochrome signal, rather than on the growth response itself.
View details for Web of Science ID A1984SY06100029
View details for PubMedID 16593476
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AUXIN CONCENTRATION GROWTH RELATIONSHIP FOR AVENA-COLEOPTILE SECTIONS FROM SEEDLINGS GROWN IN COMPLETE DARKNESS
PLANT PHYSIOLOGY
1984; 74 (2): 335-339
Abstract
A biphasic auxin dose-response curve has been obtained for indole-acetic acid (IAA)-stimulated growth of subapical sections of coleoptiles from totally dark-grown oats (Avena sativa L. cv Lodi). The curve for growth at 6 h is composed of a log-linear phase and a modified bell-shaped phase separated by a plateau. The curve is log-linear from 0.003 to 0.4 micromolar IAA when sections are incubated in pH 5.9 buffer. The plateau of IAA concentration-neutral growth is seen from 0.4 to 4.0 micromolar IAA. Further increase in growth occurs from 4.0 to 10 micromolar IAA. Changing the pH of the buffer from 5.9 to 5.5 or 6.2 changes the shape of the curve, shifting the plateau to lower IAA concentration, or abolishing it, respectively. The synthetic auxin 2,4-dichlorophenoxyacetic acid also shows a biphasic dose-response curve, but the synthetic auxin 1-naphthalene acetic acid does not. The plateau is not affected by the auxin-transport inhibitor 2,3,5-triiodobenzoic acid. The plateau is eliminated by taking sections from coleoptiles grown under continuous dim red light. We advance a model to account for these results based on two modes of auxin uptake into the cell: carrier-mediated uptake and uptake via chemiosmotic diffusion.
View details for Web of Science ID A1984SE52900027
View details for PubMedID 16663419
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PHOTOBIOLOGY OF DIAGRAVITROPIC MAIZE ROOTS
PLANT PHYSIOLOGY
1984; 75 (2): 359-363
Abstract
Light-induced modification of gravitropism in etiolated roots of Zea mays cv Bear x W38 is a low fluence response mediated by phytochrome. This cultivar has a threshold of 10(-6) mol m(-2) and becomes saturated with 10(-2) mol m(-2) of red light. The maximum light-mediated response of 32 degrees downward from horizontal occurs in roots 10 to 30 millimeters in length, 120 to 165 minutes after irradiation. Reciprocity is valid from 2 to at least 9,000 seconds and the response can be about 90% reversed by far red light. Photoreversibility is lost (;escape' occurs) about 20 minutes after red irradiation but appears to be regained 60 to 80 minutes later. A red light-induced (or synchronized) nutation in the apparent curvature rather than unusual escape characteristics may explain these results.
View details for Web of Science ID A1984SX11000016
View details for PubMedID 16663626
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FIBER OPTICS IN PLANTS
SCIENTIFIC AMERICAN
1984; 251 (2): 90-?
View details for Web of Science ID A1984TA76900011
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PHYTOCHROME-MEDIATED PHOTOTROPISM IN MAIZE SEEDLING SHOOTS
PLANTA
1984; 160 (1): 41-51
View details for Web of Science ID A1984SD93200007
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FIBER-OPTIC PLANT-TISSUES - SPECTRAL DEPENDENCE IN DARK-GROWN AND GREEN TISSUES
PHOTOCHEMISTRY AND PHOTOBIOLOGY
1984; 39 (3): 419-424
View details for Web of Science ID A1984SJ69800024
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WHY WHIP EGG-WHITES IN COPPER BOWLS
NATURE
1984; 308 (5960): 667-668
View details for Web of Science ID A1984SM02100076
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QUANTITATIVE MICROPHOTOMETRY AT THE CELLULAR-LEVEL - A SIMPLE TECHNIQUE FOR MEASURING CHLOROPLAST MOVEMENTS INVIVO
PHOTOCHEMISTRY AND PHOTOBIOLOGY
1983; 38 (3): 347-353
View details for Web of Science ID A1983RK01600013
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RHYTHMIC CHLOROPLAST MIGRATION IN THE GREEN-ALGA ULVA - DISSECTION OF MOVEMENT MECHANISM BY DIFFERENTIAL INHIBITOR EFFECTS
EUROPEAN JOURNAL OF CELL BIOLOGY
1983; 31 (1): 1-8
Abstract
The chloroplasts of the green alga, Ulva lactuca L., migrate rhythmically between the outer (periclinal) cell walls in the daytime ("face" position) and the anticlinal cell walls at night ("profile" position). Both NaN3 and colchicine inhibit chloroplast movement mainly in the direction from profile towards face position. Differential drug sensitivity is suggestive of different mechanisms for the two directions of chloroplast migration. UV light reverses the inhibition by colchicine, presumably through the formation of lumicolchicine, the non-tubulin-binding isomer of colchicine. This result is indicative of microtubule involvement. Interpretation of the effects of azide is complicated by changes in the biological clock (phase delay and lengthening of the period). Cytochalasin B has no effect on chloroplast movement when added alone, but when added with colchicine it prevents colchicine inhibition of movement. We hypothesize that chloroplast position is controlled by a balance between two opposing movement systems with differential drug sensitivity.
View details for Web of Science ID A1983RB44100001
View details for PubMedID 6617665
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PHYTOCHROME-MEDIATED CELLULAR PHOTOMORPHOGENESIS
PLANT PHYSIOLOGY
1983; 72 (3): 706-712
Abstract
Red light-induced cell elongation and division in intact, etiolated oat (Avena sativa cv Lodi) seedlings have been assessed. The middle of coleoptile was especially responsive in the very low fluence range whereas the region immediately below the coleoptile tip and the two regions just above the coleoptilar node were more responsive than the entire organ in the low fluence range. These responses in the coleoptile are both the result of an increase in cell elongation. Coleoptile cell division is slightly inhibited in the very low and slightly stimulated by red light in the low fluence range.The one-sixth of the mesocotyl closest to the node is more suppressed in its growth than is any other region in the very low fluence range. However, the low fluence response involved the entire mesocotyl equally. In the apical one-sixth of the mesocotyl, a strong suppression of cell division and a weak suppression of cell elongation occurs. In the lower five regions of the mesocotyl, red light in both fluence ranges suppresses only cell elongation. Apparently, the difference between red light-induced oat growth stimulation and suppression primarily involves differences in the response of the cell elongation process.
View details for Web of Science ID A1983RA52700022
View details for PubMedID 16663071
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BLUE-LIGHT-ABSORBING PHOTORECEPTORS IN PLANTS
PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES
1983; 303 (1116): 347-359
View details for Web of Science ID A1983RN56700001
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AUXIN TRANSPORT IN MEMBRANE-VESICLES FROM CUCURBITA-PEPO L
PLANTA
1983; 157 (3): 193-201
View details for Web of Science ID A1983QN46100001
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INITIAL EVENTS IN THE TIP-SWELLING RESPONSE OF THE FILAMENTOUS GAMETOPHYTE OF ONOCLEA-SENSIBILIS L TO BLUE-LIGHT
PLANTA
1983; 159 (4): 300-307
View details for Web of Science ID A1983RT33000002
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OPTICAL-PROPERTIES OF ETIOLATED PLANT-TISSUES
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA-BIOLOGICAL SCIENCES
1982; 79 (9): 2902-2906
Abstract
Etiolated tissues of several plants are multiple bundles of fiber optics capable of coherent transfer of light over at least 20 mm. The acceptance angles (the angles at which light can be intercepted and then internally reflected longitudinally) for mung beans, oats, and corn are 47 degrees , 59 degrees , and 52 degrees -54 degrees , respectively. The shapes of the curves that describe the acceptance angles are the same for various tissues of the same plant but differ between species. The pattern of light transmitted longitudinally through a tissue is dependent on the angle at which the light intercepts the side of the tissue and is strongly influenced by the tissue geometry. When 0.5 mm of the tip is irradiated, the amount of light traveling down the "shaded" side of the coleoptile is equal to or 2- to 3-fold greater than the amount traveling down the "lighted" side.
View details for Web of Science ID A1982NN41000035
View details for PubMedID 16593186
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EVIDENCE FROM STUDIES WITH ACIFLUORFEN FOR PARTICIPATION OF A FLAVIN-CYTOCHROME COMPLEX IN BLUE-LIGHT PHOTORECEPTION FOR PHOTOTROPISM OF OAT COLEOPTILES
PLANT PHYSIOLOGY
1982; 70 (3): 875-881
Abstract
The diphenyl ether acifluorfen enhances the blue light-induced absorbance change in Triton X100-solubilized crude membrane preparations from etiolated oat (Avena sativa L. cv. Lodi) coleoptiles. Enhancement of the spectral change is correlated with a change in rate of dark reoxidation of a b-type cytochrome. Similar, although smaller, enhancement was obtained with oxyfluorfen, nitrofen, and bifenox. Light-minus-dark difference spectra in the presence and absence of acifluorfen, and the dithionite-reduced-minus oxidized difference spectrum indicate that acifluorfen is acting specifically at a blue light-sensitive cytochrome-flavin complex. Sodium azide, a flavin inhibitor, decreases the light-induced absorbance change significantly, but does not affect the dark reoxidation of the cytochrome. Hence, it is acting on the light reaction, suggesting that the photoreceptor itself is a flavin. Acifluorfen sensitizes phototropism in dark-grown oat seedlings such that the first positive response occurs with blue light fluences as little as one-third of those required to elicit the same response in seedlings grown in the absence of the herbicide. Both this increase in sensitivity to light and the enhancement of the light-induced cytochrome reduction vary with the applied acifluorfen concentration in a similar manner. The herbicide is without effect either on elongation or on the geotropic response of dark-grown oat seedlings, indicating that acifluorfen is acting specifically close to, or at the photoreceptor end of, the stimulus-response chain. It seems likely that the flavin-cytochrome complex serves to transduce the light signal into curvature in phototropism in oats, with the flavin moiety itself serving as the photoreceptor.
View details for Web of Science ID A1982PH79500047
View details for PubMedID 16662593
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THE PHOTOPERCEPTIVE SITES AND THE FUNCTION OF TISSUE LIGHT-PIPING IN PHOTOMORPHOGENESIS OF ETIOLATED OAT SEEDLINGS
PLANT CELL AND ENVIRONMENT
1982; 5 (2): 137-145
View details for Web of Science ID A1982NL68100004
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THE EFFECT OF DELTA-AMINOLEVULINIC-ACID ON RED LIGHT-INDUCED UNROLLING OF DARK-GROWN BARLEY LEAF SECTIONS
PHYSIOLOGIA PLANTARUM
1982; 54 (2): 131-136
View details for Web of Science ID A1982ND70300006
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A BLUE LIGHT-SENSITIVE CYTOCHROME-FLAVIN COMPLEX FROM CORN COLEOPTILES - FURTHER CHARACTERIZATION
PHOTOCHEMISTRY AND PHOTOBIOLOGY
1981; 34 (6): 697-703
View details for Web of Science ID A1981MU06200007
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PARTIAL-PURIFICATION AND CHARACTERIZATION OF A BLUE LIGHT-SENSITIVE CYTOCHROME-FLAVIN COMPLEX FROM CORN MEMBRANES
PLANT PHYSIOLOGY
1981; 67 (5): 1042-1046
Abstract
A membrane fraction which contains a blue light-sensitive flavin-cytochrome complex (Brain et al. 1977 Plant Physiol 59:948) has been partially purified by sucrose and Renografin gradient centrifugations. Assays for marker enzymes show that this membrane fraction is distinct from endoplasmic reticulum, golgi, and mitochondria. This membrane fraction co-sedimented with glucan synthetase II activity, a proposed marker for plasma membrane in higher plants. The purified membrane fraction shows virtually identical light minus dark and dithionite reduced minus oxidized difference spectra with difference bands near 427 and 557 nanometers, suggesting that contamination by other cytochrome-containing membrane fractions is not significant. The photoactivity can be completely solubilized by 0.1% Triton X-100, leaving the bulk of the membrane undissolved. The kinetics for cytochrome photoreduction are not significantly affected by solubilization, indicating that both flavin and cytochrome could be associated with the same protein moiety.
View details for Web of Science ID A1981LS16900033
View details for PubMedID 16661779
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PHYTOCHROME CONTROL OF 2 LOW-IRRADIANCE RESPONSES IN ETIOLATED OAT SEEDLINGS
PLANT PHYSIOLOGY
1981; 67 (4): 733-739
Abstract
Light-induced coleoptile stimulation and mesocotyl suppression in etiolated Avena sativa (cv. Lodi) has been quantitated. Etiolated seedlings showed the greatest response to light when they were illuminated 48 to 56 hours after imbibition. Two low-irradiance photoresponses for each tissue have been described. Red light was 10 times more effective than green and 1,000 times more effective than far red light in evoking these responses. The first response, which resulted in a 45% mesocotyl suppression and 30% coleoptile stimulation, had a threshold at 10(-14) einsteins per square centimeter and was saturated at 3.0 x 10(-12) einsteins per square centimeter of red light. This very low-irradiance response could be induced by red, green, or far red light and was not photoreversible. Reciprocity failed if the duration of the red illumination exceeded 10 minutes. The low-irradiance response which resulted in 80% mesocotyl suppression and 60% coleoptile stimulation, had a threshold at 10(-10) einsteins per square centimeter and was saturated at 3.0 x 10(-8) einsteins per square centimeter of red light. A complete low-irradiance response could be induced by either red or green light but not by far red light. This response could be reversed by a far red dose 30 times greater than that of the initial red dose for both coleoptiles and mesocotyls. Reciprocity failed if the duration of the red illumination exceeded 170 minutes. Both of these responses can be explained by the action of phytochrome.
View details for Web of Science ID A1981LM91100025
View details for PubMedID 16661745
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PHYTOCHROME-MEDIATED RESPONSES IN LIGHT-GROWN CORN SHOWING RAPID, REVERSE RECIPROCITY FAILURE
PLANT CELL AND ENVIRONMENT
1981; 4 (6): 439-447
View details for Web of Science ID A1981MW83100005
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RAPID, REVERSE RECIPROCITY FAILURE FOR PHYTOCHROME CONTROL OF ITS OWN ACCUMULATION
PLANT CELL AND ENVIRONMENT
1981; 4 (6): 449-454
View details for Web of Science ID A1981MW83100006
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CORN - FUEL FOR FOOD OR FUEL FOR AUTOMOBILES
BIOSCIENCE
1981; 31 (1): 7-7
View details for Web of Science ID A1981LE73800001
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BLUE-LIGHT-INDUCED CORTICAL FIBER RETICULATION CONCOMITANT WITH CHLOROPLAST AGGREGATION IN THE ALGA VAUCHERIA-SESSILIS
PLANTA
1980; 147 (4): 355-362
View details for Web of Science ID A1980JD47700015
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PHYTOCHROME RESPONSES TO END-OF-DAY IRRADIATIONS IN LIGHT-GROWN CORN GROWN IN THE PRESENCE AND ABSENCE OF SANDOZ-9789
PLANT PHYSIOLOGY
1980; 66 (6): 1024-1026
Abstract
Corn seedlings were grown in white light in the absence and presence of the chlorosis-inducing herbicide San 9789. The resulting green and achlorophyllous seedlings were used to investigate phytochrome-mediated responses to end-of-day far red irradiation and reversal of these responses by subsequent red irradiation. Mesocotyl and coleoptile elongation increased in response to end-of-day far red irradiation, whereas the anthocyanin content of the coleoptiles was decreased. All three responses were reversible by red irradiation following the far red. Dose-response curves for far red induction and red reversal of these responses did not differ significantly for plants grown in the presence or absence of San 9789. Thus, San 9789 appears to affect neither phytochrome itself nor the response system involved. Chlorophyll screening likewise does not affect phytochrome relationships for these responses.
View details for Web of Science ID A1980KW32000002
View details for PubMedID 16661569
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INVITRO BINDING OF RIBOFLAVIN TO SUBCELLULAR PARTICLES FROM MAIZE COLEOPTILES AND CUCURBITA HYPOCOTYLS
PLANTA
1980; 147 (4): 312-319
Abstract
Saturable and reversible in vitro binding of [(14)C]riboflavin was found to occur on subcellular, sedimentable particles from maize coleoptiles and Cucurbita hypocotyls. The KD was ca. 6 μM, the pH optimum was near 6.0, and the number of binding sites amounted to 0.1-0.5 μM on a fresh-weight basis. When the reducing agent dithionite was present, riboflavin binding increased-the KD was 2.5 μM, and the pH optimum above 8.0. The binding was specific: flavin mononucleotide (FMN) and flavin adenosine-dinucleotide (FAD) bound less tightly to these sites than riboflavin and another major soluble flavin, the previously described riboflavin-analog "FX", occurring in grass coleoptiles. These flavin-binding sites were localized on vesicles derived from plasmalemma and endoplasmic reticulum by analyzing sucrose and metrizamide density gradients and marker enzymes.
View details for Web of Science ID A1980JD47700009
View details for PubMedID 24311081
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CHARACTERIZATION OF THE RED-LIGHT INDUCED REDUCTION OF A PARTICLE ASSOCIATED B-TYPE CYTOCHROME FROM CORN IN THE PRESENCE OF METHYLENE-BLUE
PHOTOCHEMISTRY AND PHOTOBIOLOGY
1980; 32 (5): 669-677
View details for Web of Science ID A1980KP71800015
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LIGHT-INDUCIBLE CYTOCHROME REDUCTION IN MEMBRANE PREPARATIONS FROM CORN COLEOPTILES .1. STABILIZATION AND SPECTRAL CHARACTERIZATION OF THE REACTION
PLANT PHYSIOLOGY
1980; 66 (6): 1067-1073
View details for Web of Science ID A1980KW32000011
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ACTIN AND CORTICAL FIBER RETICULATION IN THE SIPHONACEOUS ALGA VAUCHERIA-SESSILIS
PLANTA
1980; 147 (4): 363-375
View details for Web of Science ID A1980JD47700016
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SOLUBILIZED AUXIN-BINDING PROTEIN - SUBCELLULAR-LOCALIZATION AND REGULATION BY A SOLUBLE FACTOR FROM HOMOGENATES OF CORN SHOOTS
PLANTA
1979; 146 (3): 263-270
View details for Web of Science ID A1979HL35100003
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RED LIGHT-INDUCED REDUCTION OF A PARTICLE-ASSOCIATED B-TYPE CYTOCHROME FROM CORN IN THE PRESENCE OF METHYLENE-BLUE
PHOTOCHEMISTRY AND PHOTOBIOLOGY
1979; 29 (2): 359-365
View details for Web of Science ID A1979GJ35000018
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PHYTOCHROME PHOTOREVERSIBILITY - EMPIRICAL-TEST OF HYPOTHESIS THAT IT VARIES AS A CONSEQUENCE OF PIGMENT COMPARTMENTATION
PLANTA
1978; 141 (2): 129-134
View details for Web of Science ID A1978FG10400002
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PROPERTIES OF A SOLUBILIZED MICROSOMAL AUXIN-BINDING PROTEIN FROM COLEOPTILES AND PRIMARY LEAVES OF ZEA-MAYS
PLANT PHYSIOLOGY
1978; 62 (1): 152-157
Abstract
An auxin-binding protein can be solubilized from microsomal membranes of Zea mays using either Triton X-100 extraction of the membranes or buffer extraction of the acetone-precipitated membranes. This paper describes the properties of the binding protein solubilized by these two methods. The binding is assayed by gel filtration chromatography in the presence of naphthalene [2-(14)C]acetic acid. Binding is rapid and reversible with an optimum at pH 5. Both preparations show similar molecular weights by gel filtration (80,000 daltons) at pH 7.6 and 0.1 molar NaCl, and both aggregate at low ionic strength. They appear to be the same active molecular species. The binding activity is destroyed by trypsin, pronase or para-chloromercuribenzoic acid, but not significantly reduced by phospholipase C, DNase, RNase, or dithioerythritol. Since saturating amounts of naphthalene acetic acid protect the molecule from inhibition by para-chloromercuribenzoic acid, it is concluded that the binding protein has a sulfhydryl group at the binding site, or protects such a group in its binding conformation. The dissociation constant of the protein for naphthalene acetic acid is 4.6 x 10(-8) molar with 30 picomoles of sites per gram of tissue fresh weight. Binding constants were estimated for 13 other natural and synthetic auxins by competition with naphthalene[2-(14)C]acetic acid. Their dissociation constants are in general agreement with published values for their binding to intact membranes and their biological activity, although several exceptions were noted. A supernatant factor from the same tissue changes the apparent affinity of the protein for naphthalene acetic acid. This factor may be the same one as has been previously reported to alter the affinity of intact microsomes for auxin.
View details for Web of Science ID A1978FJ89000035
View details for PubMedID 16660457
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APPLICATION OF HIGHER DERIVATIVE TECHNIQUES TO ANALYSIS OF HIGH-RESOLUTION THERMAL-DENATURATION PROFILES OF REASSOCIATED REPETITIVE DNA
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1978; 75 (12): 6026-6030
Abstract
We have analyzed high-resolution denaturation profiles of reassociated repetitive DNA sequences by using a combination of higher derivative analysis and curve-fitting techniques. Procedures originally used for resolution of components in complex absorption spectra were found to be applicable to high-resolution analysis of melting profiles of reassociated repetitive DNA sequences from pea DNA. Under conditions that eliminate the base composition effect on thermal stability (2.4 M tetraethylammonium chloride), such an anlysis can distinquish "thermal classes" of repetitive DNA duplexes exhibiting different amounts of base pair mismatch. Only a single thermal class is observed in reassociated Escherichia coli DNA whereas at least five classes can be reproducibly distinguished in pea and mung bean DNAs.
View details for Web of Science ID A1978GC25200062
View details for PubMedID 366608
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AUXIN RECEPTORS OF MAIZE COLEOPTILE MEMBRANES DO NOT HAVE ATPASE ACTIVITY
PLANT PHYSIOLOGY
1978; 61 (4): 581-584
Abstract
Membrane-localized auxin-binding sites from coleoptiles and primary leaves of Zea mays L. which may be auxin receptors can be fully solubilized by 1 to 1.5 mg of Triton X-100 per mg of membrane protein (about 1 mg per gram of original tissue fresh weight), while 70% of the basal (Mg(2+))-ATPase and 85% of the K(+)-stimulated (Mg(2+))-ATPase (pH 6) remain pelletable. Gel exclusion chromatography on Bio-Gel A-1.5m indicates that the solubilized receptors occur as detergent-protein micelles of about 90,000 daltons equivalent molecular weight. Solubilized ATPase activities occur (a) as very large particles excluded from the gel, and (b) as particles of a size substantially smaller than the particles that exhibit auxin binding. The auxin-binding receptor therefore appears not to be an ATPase.
View details for Web of Science ID A1978EY11600022
View details for PubMedID 16660340
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INTRACELLULAR PHYTOCHROME DISTRIBUTION AS A FUNCTION OF ITS MOLECULAR FORM AND OF ITS DESTRUCTION
AMERICAN JOURNAL OF BOTANY
1978; 65 (6): 671-676
View details for Web of Science ID A1978FN78300010
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CHARACTERIZATION OF A MEMBRANE FRACTION CONTAINING A B-TYPE CYTOCHROME
PLANT PHYSIOLOGY
1977; 59 (5): 941-947
Abstract
The various components obtained from etiolated corn (Zea mays L.) coleoptiles were fractionated by differential or sucrose gradient centrifugation. The endoplasmic reticulum, proplastids, Golgi, and mitochondria were localized by enzymic or other markers in the various fractions. A fifth fraction was also characterized. It contains glucan synthetase II activity, binding sites for N-naphthylphthalamic acid, NADH dehydrogenase activity which is both antimycin A- and cyanide-insensitive, and a b-type cytochrome. It is possible that this fraction is plasma membrane and that it may contain the blue-ultraviolet photoreceptor for phototropism in corn.
View details for Web of Science ID A1977DG68600033
View details for PubMedID 16659973
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LABELING OF MEMBRANES FROM ERYTHROCYTES AND CORN WITH FLUORESCAMINE
BIOCHIMICA ET BIOPHYSICA ACTA
1977; 471 (1): 67-77
Abstract
Fluorescamine was used as a fluorescent label for intact human erythrocytes and slices of corn coleoptile tissue. This reagent has a greater affinity for membranous than for soluble proteins, and also labels membrane lipids which contain primary amine groups. In addition, some membrane fractions from labeled coleoptiles have a higher affinity for fluorescamine than do others. The relative labeling of the various fractions can be altered by changing the pH of the external labeling medium. Because the pH of the medium determines the rate of hydrolysis of fluorescamine to an unreactive form, this result suggests that the specificity of this reagent towards different cellular structures is determined by the lifetime of the active reagent. Fluorescamine was not found to be a specific reagent for the cell surface.
View details for Web of Science ID A1977EB05100008
View details for PubMedID 921976
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CIRCADIAN-RHYTHMS OF CHLOROPLAST ORIENTATION AND PHOTOSYNTHETIC CAPACITY IN ULVA
PLANT PHYSIOLOGY
1976; 58 (1): 22-27
Abstract
Ulva lactuca L. var. latissima (L.) Decandolle and var. rigida (C. Agardh) Le Jolis and U. mutabilis Foyn have a circadian rhythm of chloroplast orientation which results in large changes in the light-absorption properties of the thallus. During the day, the chloroplasts cover the outer face of the cells and absorbance is high. At night, the chloroplasts are along the side walls and absorbance is low. Enteromorpha linza (L.) J. Agardh, E. intestinalis (L.) Link, E. sp., and Monostroma grevillei (Thuret) Wittrock, members of the Ulvales, were not observed to have this rhythmic movement. Chloroplasts, when in the face position, could not be induced to move to the sides by high intensity light up to 80,000 lux. Unrelated to chloroplast position per se and light-absorption efficiency, there is a rhythm of photosynthetic capacity which peaks just before midday and which continues in constant darkness.
View details for Web of Science ID A1976BY81100005
View details for PubMedID 16659613
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AUTOMATIC MONITORING OF A CIRCADIAN-RHYTHM OF CHANGE IN LIGHT TRANSMITTANCE IN ULVA
PLANT PHYSIOLOGY
1976; 58 (1): 17-21
Abstract
Ulva lactuca L. var. latissima (L.) DeCandolle has a circadian rhythm of visible light transmittance change which is caused by chloroplast orientation. With a continuously recording microphotometer system, clear rhythms could be monitored for up to 10 days. Measuring beam intensity effects on the free running period were seen down to 10(-7) w cm(-2). While these effects complicate the measuring process, they demonstrate that Ulva is very sensitive to light. The free running period in constant darkness at 20 C is 24 to 25 hours. The position in the cell occupied by the chloroplasts when the rhythm damps out can be influenced by light. A method is described by which the times of rhythm maxima can be calculated accurately and objectively from a relatively small number of points.
View details for Web of Science ID A1976BY81100004
View details for PubMedID 16659612
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REVERSIBLE REDISTRIBUTION OF PHYTOCHROME WITHIN CELL UPON CONVERSION TO ITS PHYSIOLOGICALLY ACTIVE FORM
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1975; 72 (3): 799-803
Abstract
The intracellular localization of phytochrome was seen in dark-grown oat (Avena sativa L., cv. Garry) and rice (Oryza sativa L., cv. unknown) shoots after various light treatments using an indirect peroxidase-antiperoxidase antibody labeling method. Phytochrome is generally distributed throughout the cytoplasm in cells of tissue that had not been exposed to light prior to fixation. Within, at most, 8 min after the onset of saturating red irradiation, phytochrome, now present in the far-red-absorbing form, becomes associated with discrete regions of the cell. These regions do not appear to be nuclei, plastids, or mitochondria. After phototransformation back to the red-absorbing form originally present, phytochrome slowly resumes its general distribution. It is possible that this discrete localization of the far-red-absorbing form of phytochrome represents a physiologically significant binding with a receptor site in the cell.
View details for Web of Science ID A1975W171200006
View details for PubMedID 1093170
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The isolation and partial characterization of a membrane fraction containing phytochrome.
Plant physiology
1974; 54 (3): 263-271
Abstract
If 4-day-old dark-grown zucchini squash seedlings (Cucurbita pepo L. cv. Black Beauty) are exposed briefly to red light, subsequent cell fractionation yields about 40% of the total extractable phytochrome in the far red-absorbing form bound to a particulate fraction. The amount of far red-absorbing phytochrome in the pellet is strongly dependent on the Mg concentration in the extraction medium. The apparent density of the Pfr-containing particles following sedimentation on sucrose gradients corresponds to 15% (w/w) sucrose with 0.1 mm Mg and 40% sucrose with 10 mm Mg. This particulate fraction could be readily separated from mitochondria and other particulate material by taking advantage of these apparent density changes with changes in Mg concentration. Electron microscopy of negatively stained preparations shows that with 1 mm Mg only minute particles are present. These were too small to reveal structural detail with this technique. With 3 mm Mg, separate membranous vesicles between 400 and 600 Angstroms in diameter appear. At higher Mg concentrations, the vesicles aggregate, causing obvious turbity. The effect of Mg on vesicle formation and aggregation is completely reversible. Above 10 mm Mg, vesicle aggregation persists, but the percentage of bound Pfr decreases.
View details for PubMedID 16658871
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INVIVO PROPERTIES OF MEMBRANE-BOUND PHYTOCHROME
PLANT PHYSIOLOGY
1974; 54 (3): 272-276
Abstract
After a 3-minute irradiation with red light, which saturates the phototransformation from the red light-absorbing form of phytochrome to the far red light absorbing form of phytochrome, about 40% of the phytochrome extractable from hooks of etiolated squash seedlings (Cucurbita pepo L. cv. Black Beauty) can be pelleted as Pfr at 17,000g after 30 minutes. Dark controls yield only 2 to 4% pelletable phytochrome in the form Pr. If a dark period intervenes between red irradiation and extraction, the bound Pfr gradually loses its photoreversibility. The time course for this destruction parallels the time course for phytochrome destruction in vivo following saturating red irradiation. The soluble fraction of phytochrome remains constant. These results suggest that in squash seedlings phytochrome destruction is related exclusively to the fraction which becomes membrane-bound. The induction of phytochrome binding by red light is not completely reversible by far red. In plants given saturating red followed immediately by saturating far red light, 12% of the phytochrome is found in the bound fraction as Pr if the phytochrome extraction is immediate. If a dark period intervenes between red-far red treatment and extraction, the bound phytochrome is released within 2 hours. A model of the binding properties of phytochrome, based on molecular interaction at the membrane is proposed, and possible consequences for the mechanism of action of phytochrome are discussed.
View details for Web of Science ID A1974U247500010
View details for PubMedID 16658872
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ISOLATION AND PARTIAL CHARACTERIZATION OF A MEMBRANE FRACTION CONTAINING PHYTOCHROME
PLANT PHYSIOLOGY
1974; 54 (3): 263-271
View details for Web of Science ID A1974U247500009
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PHYTOCHROME - PLANT LIGHT SENSOR AND PHOTOSWITCH
ANAIS DA ACADEMIA BRASILEIRA DE CIENCIAS
1973; 45: 85-92
View details for Web of Science ID A1973AH55700012
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BINDING PROPERTIES IN-VITRO OF PHYTOCHROME TO A MEMBRANE FRACTION
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
1973; 70 (12): 3861-3865
Abstract
Brief irradiation of a buffer extract of dark-grown zucchini squash seedlings with red light results in the binding of the far-red-absorbing form of phytochrome to a particulate fraction. A low concentration of magnesium (0.1 mM) permits partial far-red reversal of the binding. A higher concentration (10 mM) yields actually enhanced binding after the far-red treatment. Both magnesium and calcium have a strong effect on the vesicularization of the phytochrome-binding particles and on their aggregation into readily sedimentable complexes. At concentrations above 10 mM, binding of the far-red-absorbing form of phytochrome is inhibited. These effects were not observed with sodium or potassium. Increasing the H(+) concentration led to increased binding of the far-red-absorbing form. This form of phytochrome bound at pH 6.5 and 10 mM magnesium is released if either the pH is raised to 8.0 or the magnesium concentration is raised to 50 mM. These properties suggest a new method for phytochrome purification.
View details for Web of Science ID A1973S009100038
View details for PubMedID 16592127
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IN-VIVO PHYTOCHROME REVERSION IN IMMATURE TISSUE OF ALASKA PEA SEEDLING
PLANT PHYSIOLOGY
1971; 48 (1): 46-?
Abstract
Reversion of far red-absorbing phytochrome to red-absorbing phytochrome without phytochrome destruction (that is, without loss of absorbancy and photoreversibility) occurs in the following tissues of etiolated Alaska pea seedlings (Pisum sativum L.): young radicles (24 hours after start of imbibition), young epicotyls (48 hours after start of imbibition), and the juvenile region of the epicotyl immediately subjacent to the plumule in older epicotyls. Reversion occurs rapidly in the dark during the first 30 minutes following initial phototransformation of red-absorbing phytochrome to far red-absorbing phytochrome. If these tissues are illuminated continuously with red light for 30 minutes, the total amount of phytochrome remains unchanged. Beyond 30 minutes after a single phototransformation or after the start of continuous red irradiation, phytochrome destruction commences. In young radicles, sodium azide inhibits this destruction, but does not affect reversion. In older tissues in which far red-absorbing phytochrome destruction begins immediately upon phototransformation, strong evidence for simultaneous far red-absorbing phytochrome reversion is obtained from comparison of far red-absorbing phytochrome loss in the dark following a single phototransformation with far red-absorbing phytochrome loss under continuous red light.
View details for Web of Science ID A1971J920300010
View details for PubMedID 16657731
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PHYTOCHROME APPEARANCE AND DISTRIBUTION IN EMBRYONIC AXIS AND SEEDLING OF ALASKA PEAS
PLANTA
1970; 91 (2): 146-?
Abstract
Apparent synthesis of phytochrome has been observed in the embryonic axis of germinating Alaska pea and in the young seedling. The onset of photoreversibility can be delayed, and the amount of phytochrome appearing in a plant of a given size somewhat decreased, by treatment with cycloheximide in appropriate concentrations. Similar concentrations of cycloheximide also reduce elongation. Soaking seeds in water at 4° for 24 hr also prevents the onset of photoreversibility in the embryonic axis. The pattern of phytochrome appearance, and the distribution of relative amounts of phytochrome, suggest that synthesis may be closely related to general protein synthesis during elongation.
View details for Web of Science ID A1970F928700005
View details for PubMedID 24500016
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GIBBERELLIN AND CCC EFFECTS ON FLOWERING AND GROWTH IN LONG-DAY PLANT LEMNA GIBBA G3
PLANT PHYSIOLOGY
1969; 44 (4): 503-?
Abstract
The application of gibberellic acid (GA(3)) to the non-rosette long-day plant Lemna gibba G3 at concentrations from 0.1 to 100 mg/l did not induce flowering on short days and inhibited flowering on long days at concentrations of 1 mg/l and higher. On both short and long days GA(3) concentrations above 1 mg/l caused a decrease in frond size and fresh and dry weight, but an increase in the rate of frond production and thus an increase in the # VF (number of vegetative fronds). Identical results were obtained when gibberellin A(7) was used instead of GA(3).The addition of the plant growth retardant CCC [(2-chloroethyl) trimethylammonium chloride] to the culture medium on long days resulted in almost complete inhibition of flowering at 10(-3) M. Vegetative growth was also inhibited to some extent. With CCC at 10(-3) M the simultaneous addition of GA(3) resulted in partial reversal of flower inhibition with 0.3 mg/l GA(3) being optimal. The inhibition of vegetative growth as measured by fresh and dry weight was also partially reversed by GA(3), but the threshold concentration for reversal of flower inhibition was at least 10 times lower than that for inhibition of vegetative growth.These results are interpreted as indicating that gibberellins are important for flowering in the non-rosette long-day plant L. gibba G3, but apparently are present in non-limiting concentrations on short days.
View details for Web of Science ID A1969D255000006
View details for PubMedID 16657092
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EFFECT OF LOW-INTENSITY RED AND FAR-RED LIGHT AND HIGH-INTENSITY WHITE LIGHT ON FLOWERING RESPONSE OF LONG-DAY PLANT LEMNA GIBBA G3
PLANT PHYSIOLOGY
1968; 43 (2): 157-?
Abstract
The long-day plant Lemna gibba L., strain G3 exhibits a relatively low sensitivity to short, white-light interruptions given during the dark period of a short-day cycle. However, the plants are fairly sensitive to low-intensity red light treatments given during a 15-hour dark period on the third day of a 2LD-(9L:15D)-2LD-7SD schedule. Far-red light is almost as effective as red light, and attempts to reverse the red light response with subsequent far-red light treatments have not been successful. Blue light proved to be without effect. When plants were grown on a 48-hour cycle with 15 minutes of red light every 4 hours during the dark period, the critical daylength was reduced from about 32 hours to slightly less than 12 hours.Continuous red light induced a fairly good flowering response. However, as little as 1 hour of white light each day gave a significant improvement in the flowering response over that of the continuous red light control. White light of 600 to 700 ft-c was more effective than white light of 60 to 70 ft-c. The white light was much more effective when divided into 2 equal exposures given 8 to 12 hours apart. These results suggest an increase in light sensitivity with regard to flower induction about 8 to 10 hours after the start of the light period.
View details for Web of Science ID A1968A781900004
View details for PubMedID 16656749
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SOME PROPERTIES OF PHYTOCHROME ISOLATED FROM DARK-GROWN OAT SEEDLINGS (AVENA SATIVA L)
PLANT PHYSIOLOGY
1968; 43 (8): 1239-?
Abstract
Phytochrome was partially purified from etiolated seedlings of Avena sativa L. Several properties of the red-absorbing (P(R)) and far-red absorbing (P(FR)) forms of the pigment were compared. The 2 forms could not be shown to differ with respect to their sedimentation velocity in sucrose density gradients, elution volume from Sephadex G-200 columns, binding properties on calcium phosphate, or electrophoretic mobility. P(FR), however, was more labile than P(R) during precipitation with 50% ammonium sulfate. Sephadex G-200 elution diagrams obtained with fresh phytochrome preparations revealed 2 components of different molecular weights, 1 roughly 180,000, and 1 roughly 80,000. Native phytochrome had an absorption spectrum in vivo showing an absorption maximum for P(R) of 667 nm. Both the large and small forms of phytochrome mentioned above can be maintained with an absorption maximum for P(R) of 667 nm. However, allowing them to remain for several hours as P(FR), even at 4 degrees , shifted this peak to 660 nm. The protein conformational change during phytochrome transformation may be quite small, though the various comparative techniques used do not strictly rule out a fairly large one. The need for maintaining the pigment as P(R) during all steps of purification, but particularly during ammonium sulfate precipitation is underscored.
View details for Web of Science ID A1968B732200008
View details for PubMedID 16656907
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EFFECTS OF LIGHT ON A CIRCADIAN RHYTHM OF CONIDIATION IN NEUROSPORA
PLANT PHYSIOLOGY
1967; 42 (11): 1504-?
Abstract
The expression of a circadian rhythm of conidiation by timex, a strain of Neurospora crassa, is inhibited by growth in continuous white light. The action spectrum for this effect has a strong peak (with minor subpeaks) in the blue region of the visible spectrum, and a broad shoulder in the near ultraviolet. This action spectrum suggests that a carotenoid or flavin compound may be the photoreceptor, but does not allow one to determine conclusively whether the receptor is indeed a carotenoid, flavin, or some other unrelated pigment. Two lines of evidence suggest that a carotenoid is not the photoreceptor. First, the in vivo absorption spectrum of timex (representing the sum of the spectra of the individual pigments present, predominantly carotenoids) has peaks at wavelengths 10 to 20 mmu longer than those of the action spectrum peaks. Second, an albino-timex has normal photosensitivity, a situation requiring that the photoreceptor, if carotenoid, be a quantitatively minor constituent of the total carotenoid complement.The magnitude and direction of phase-shift resulting from a standard dose of white light given at different times in the daily cycle of timex varies in the manner reported for other organisms. Additional phase-shift experiments have shown that there are no major transients in the attainment of a new equilibrium after a phase-shifting perturbation, and that 2 light reactions (rapidly and slowly saturating) may be involved in the phase-shift response.
View details for Web of Science ID A1967A301400008
View details for PubMedID 16656687
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FLOWERING RESPONSES OF LONG-DAY PLANT LEMNA GIBBA G3
PLANT PHYSIOLOGY
1967; 42 (11): 1553-?
Abstract
Lemna gibba L., strain G3, exhibits a qualitative long-day flowering response with a critical daylength on a 24-hour cycle of about 10 hours. Evidence is presented that the onset of daughter frond formation in a given frond inhibits the activity of the flowering meristem. Consequently, flower induction can only occur in fronds smaller than about 0.05 to 0.07 mm long. Although a minimum of 1 long day seems to be sufficient to induce the formation of flower primordia, at least 6 long days are required to obtain mature flowers since long days are also required for the early stages of flower development. The critical night length on 24, 48 and 72-hour cycles is respectively 14, 16, and 18 to 22 hours. The close similarity between the critical night length for the different cycle lengths is explained in terms of an inhibitory effect of darkness both on flower initiation and flower development. A 10-hour dark period is more inhibitory to flowering on a 36-hour cycle than on 24, 48, 60 or 72-hour cycles. It is suggested that darkness inhibits flowering through the formation of a light-labile flower inhibitor which acts to inhibit the functioning of the flowering stimulus.
View details for Web of Science ID A1967A301400014
View details for PubMedID 16656692
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PHOTOCHEMICAL AND NONPHOTOCHEMICAL REACTIONS OF PHYTOCHROME IN VIVO
PLANT PHYSIOLOGY
1966; 41 (3): 467-?
Abstract
The nonphotochemical reactions of phytochrome in the coleoptiles of dark-grown corn seedlings were studied at 3 temperatures: 14 degrees , 24 degrees , and 34 degrees . The data obtained show that the destruction of P(fr) is the only measurable reaction occurring; reversion of P(fr) to P(r) was not found. The Q(10)'s (2.7 and 3.5) and zero order kinetics found for the destruction reaction are consistent with the hypothesis that the reaction is enzyme-mediated.In vivo action spectra for phytochrome transformation in the coleoptiles of darkgrown corn seedlings were obtained which agree qualitatively with those obtained by other workers for phytochrome-mediated physiological responses and in vitro action spectra. In vivo conversion of phytochrome by blue light, as determined from spectrophotometric measurements of phytochrome itself, is reported. Action peaks for P(r) were found at 667 mmu and in the blue in the region of 400 mmu, with a broad shoulder from 590 mmu to 640 mmu. Action peaks for P(fr) were found at 725 mmu and in the blue in the region of 400 mmu with a minor peak at 670 mmu, and a broad shoulder from 590 mmu to 640 mmu. The ratio of the quantum efficiencies of P(r) at 667 mmu and P(fr) at 725 mmu (Phi(r667)/Phi(fr725)) was estimated to be 1.0.
View details for Web of Science ID A19667557300027
View details for PubMedID 16656277
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EFFECT OF RED LIGHT ON PHOTOTROPIC SENSITIVITY OF CORN COLEOPTILES
PLANT PHYSIOLOGY
1966; 41 (10): 1715-?
Abstract
The effect of red light in alteration of the phototropic sensitivity of corn coleoptiles (Zea mays L., cultivar Burpee Barbecue Hybrid) is investigated. Phototropic dosage-response curves for etiolated coleoptiles are compared with those for coleoptiles receiving 1 hour of continuous red light immediately prior to phototropic induction. In the former case, only curvature comparable to the first positive curvature of oat coleoptiles is obtained. There is no evidence for first negative curvature and only minimal second positive curvature. The reciprocity law proved valid for all curvatures obtained. With red light, the sensitivity of the first positive curvature was decreased over ten-fold and there was clear appearance of second positive curvature for which the reciprocity law was not valid. Once again there was no evidence for negative curvature. Time course studies indicated that within 1 hour of the beginning of red light treatment at 25 degrees , reactions leading to the decrease in phototropic sensitivity of the first positive component had gone to completion whether the red light was continuous or consisted of a single 1 second exposure followed by a 1 hour dark period. An action spectrum for the red-induced change in phototropic sensitivity showed a marked peak near 660 mmu with a small broad shoulder between 610 and 630 mmu, characteristic of phytochrome-mediated responses. The effect of red light could be fully reversed by low dosages of far-red light, but longer doses of far red were less effective. Large dosages of far-red light alone induced the same alteration in phototropic sensitivity as did red light.
View details for Web of Science ID A19668761800024
View details for PubMedID 16656463
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PHYSIOLOGICAL VERSUS SPECTROPHOTOMETRIC STATUS OF PHYTOCHROME IN CORN COLEOPTILES
PLANT PHYSIOLOGY
1966; 41 (7): 1159-?
Abstract
The influence of red light in altering the phototropic sensitivity of corn coleoptiles (Zea mays L., cultivar Burpee Barbecue Hybrid) is compared with the spectrophotometric status of the phytochrome they contain. The distribution of measurable phytochrome corresponds roughly with the distribution of sensitivity to red light for physiological change. Both phytochrome concentration and red light sensitivity are maximal in the coleoptile tips. Red light pretreatments which reduce total phytochrome by about 50%, however, do not alter subsequent red light sensitivity of the phototropic system. Dosages of red light sufficient to saturate the physiological system are two orders of magnitude too small to induce measurable phytochrome transformation. The log-dosage-response curves for physiological change and for phytochrome transformation do not have the same slopes. The time course for appearance, mainconcentration of the far-red-absorbing form of phytochrome over a broad range of tenance, and decay of the physiological response is independent of the measurable concentrations. The following hypothesis is proposed: the phytochrome mediating the alteration in phototropic sensitivity is only a small proportion of the total present. This small active fraction is physically and kinetically independent of the bulk measurable, and is packaged in some manner which facilitates its transformation in both directions.
View details for Web of Science ID A19668270600013
View details for PubMedID 16656379
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DISTRIBUTION OF PHYTOCHROME IN ETIOLATED SEEDLINGS
PLANT PHYSIOLOGY
1965; 40 (5): 934-?
View details for Web of Science ID A19656843400030
View details for PubMedID 16656178
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PHOTOTROPIC DOSAGE-RESPONSE CURVES FOR OAT COLEOPTILES
PLANT PHYSIOLOGY
1963; 38 (3): 248-?
View details for Web of Science ID A19631862C00017
View details for PubMedID 16655780
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A KINETIC MODEL FOR PHOTOTROPIC RESPONSES OF OAT COLEOPTILES
PLANT PHYSIOLOGY
1963; 38 (3): 253-?
View details for Web of Science ID A19631862C00018
View details for PubMedID 16655781
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MEDIATION OF PHOTOTROPIC RESPONSES OF CORN COLEOPTILES BY LATERAL TRANSPORT OF AUXIN
PLANT PHYSIOLOGY
1963; 38 (3): 237-?
View details for Web of Science ID A19631862C00003
View details for PubMedID 16655779
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PHOTOMORPHOGENETIC RESPONSES OF SPORELINGS OF MARSILEA VESTITA
PLANT PHYSIOLOGY
1962; 37 (2): 142-?
View details for Web of Science ID A19621855C00012
View details for PubMedID 16655622
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MEDIATION OF GEOTROPIC RESPONSE BY LATERAL TRASSPORT OF AUXIN
PLANT PHYSIOLOGY
1961; 36 (3): 364-?
View details for Web of Science ID A19611850C00004
View details for PubMedID 16655523
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KINETIN MODIFICATION OF SPORELING ONTOGENY IN MARSILEA VESTITA
AMERICAN JOURNAL OF BOTANY
1961; 48 (5): 369-?
View details for Web of Science ID A19612639A00006
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LIGHT DOSAGE AND PHOTOTROPIC RESPONSES OF CORN AND OAT COLEOPTILES
PLANT PHYSIOLOGY
1960; 35 (6): 951-962
View details for Web of Science ID A1960WC97300027
View details for PubMedID 16655448