[The strange lightness of quality...].
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Cardiology↗
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A novel mechanism of nuclear photosynthesis gene regulation by redox signals from the chloroplast during photosystem stoichiometry adjustment.
Photosynthetic organisms acclimate to long term changes in the environmental light quality by an adjustment of their photosystem stoichiometry to maintain photosynthetic efficiency. By using light sources that predominantly excite either photosystem I (PSI) or photosystem II (PSII), we studied the effects of excitation imbalances between both photosystems on nuclear PSI gene transcription in transgenic tobacco seedlings with promoter::beta-glucuronidase gene fusions. Shifts from PSI to PSII light sources (and vice versa) induced changes in the reduction/oxidation state of intersystem redox components, and acclimation of tobacco seedlings to such changes were monitored by changes in chlorophyll a/b ratios and in vivo chlorophyll a fluorescence. The ferredoxin-NADP(+)-oxidoreductase gene promoter did not respond to these treatments, those from the genes for subunits PsaD and PsaF of PSI are activated by a reduction signal, and the plastocyanin promoter responded to both reduction and oxidation signals. Additional experiments with photosynthetic electron transport inhibitors 3-(3',4'-dichlorophenyl)-1,1'-dimethyl urea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone demonstrated that the redox state of the plastoquinone pool controls the activity of the plastocyanin promoter, whereas subunit PsaD and PsaF gene transcription is regulated by other photosynthesis-derived signals. Thus, the expression of nuclear-encoded PSI genes is controlled by diverse light quality-dependent redox signals from the plastids during photosystem stoichiometry adjustment.
Binding Sites↗
A comparison of phenotypic plasticity in the native dandelion Taraxacum ceratophorum and its invasive congener T. officinale.
We compared plastic responses to variation in the light environment for sympatric populations of native and exotic dandelion species, Taraxacum ceratophorum and Taraxacum officinale. Plasticity in leaf size, inflorescence height, reproductive phenology and dispersal-related traits were measured under experimentally altered light quality (red : far-red light ratio, R : FR) and light intensity (photosynthetically active radiation, PAR). To test whether differences in means and reaction norms of dispersal-related traits between species affected colonization potential, we created seed-dispersal models based on seed-fall rate and release height. Differences in plasticity between species were not systematic, but varied in direction and magnitude among traits. Taraxacum officinale produced larger leaves that exhibited greater plasticity in size under variable light intensity than T. ceratophorum. Plasticity in scape length at flowering occurred in relation to R : FR ratio in both species, but tended to be greater in T. ceratophorum. Seed-bearing scapes of T. officinale were taller and more canalized in height across light regimes than scapes of T. ceratophorum. Seeds of T. officinale were smaller than seeds of T. ceratophorum. Models predict greater dispersal in T. officinale within open and vegetated habitats. In contrast to the idea that plasticity promotes invasiveness, results suggest that the lack of plasticity in dispersal-related traits enhances the colonization potential of T. officinale.
Adaptation, Physiological↗
Interaction of phytochromes A and B in the control of de-etiolation and flowering in pea.
The interactions of phytochrome A (phyA) and phytochrome B (phyB) in the photocontrol of vegetative and reproductive development in pea have been investigated using null mutants for each phytochrome. White-light-grown phyA phyB double mutant plants show severely impaired de-etiolation both at the seedling stage and later in development, with a reduced rate of leaf production and swollen, twisted internodes, and enlarged cells in all stem tissues. PhyA and phyB act in a highly redundant manner to control de-etiolation under continuous, high-irradiance red light. The phyA phyB double mutant shows no significant residual phytochrome responses for either de-etiolation or shade-avoidance, but undergoes partial de-etiolation in blue light. PhyB is shown to inhibit flowering under both long and short photoperiods and this inhibition is required for expression of the promotive effect of phyA. PhyA is solely responsible for the promotion of flowering by night-breaks with white light, whereas phyB appears to play a major role in detection of light quality in end-of-day light treatments, night breaks and day extensions. Finally, the inhibitory effect of phyB is not graft-transmissible, suggesting that phyB acts in a different manner and after phyA in the control of flower induction.
Genes, Plant↗
Regulation of nuclear genes encoding chloroplast proteins in transgenic plants.
Transgenic plants have been particularly useful in studying nuclear genes encoding for photosynthetic functions. The expression of these genes and their chimeric constructs in transgenic plants faithfully mimics their natural counterparts. The use of sensitive chimeric reporter genes has enabled localizing the activity of genes encoding photosynthetic proteins to individual cells. Cab and rbcS transgenes have been shown to retain sensitivity to light quality, which is modulated by phytochrome. Conditional light activation under the influence of a circadian rhythm has been shown for Cab transgenes. Transgenic plants containing truncated promoters have helped delineate cis-regulatory positive and negative elements involved in light-mediated transcriptional induction and tissue specificity.
Base Sequence↗
Functional characteristics of chlorophyll d-predominating photosynthetic apparatus in intact cells of Acaryochloris marina.
Functional organization of the photosynthetic apparatus in the unique chlorophyll d-predominating prokaryote, Acaryochloris marina, was studied using polarographic measurements of single-turnover flash yields, action spectra and optical cross sections for PS-specific reactions. O(2) evolution was indicative of PS II activity, while reversible photoinhibition of respiratory O(2) uptake under aerobic conditions in the presence of DCMU and H(2) photoevolution by anaerobically adapted cells were the indicatives of PS I activity. O(2) evolution in the cells upon single-turnover flashes followed the normal S-state cycle with a period-4 oscillation. Analysis of action spectra for the partial reactions of photosynthesis revealed that: (1) distinct spectral forms of Chl d are nonuniformly distributed between PS I and PS II, e.g. Chl d-695 and Chl d-735 are preferentially located in PS II and PS I, respectively; (2) a minor fraction of Chl a in the cells belongs mostly to PS II; (3) biliproteins transfer excitation energy both to PS II and, with a lower efficiency, PS I; (4) the efficiency of energy transfer from biliproteins to PS II depends on the light quality growth conditions and is larger in white light (WL)-grown cells compared to the red light (RL)-grown cells. Content of functional O(2) evolving PS II centers decreases 2 times in the RL-grown cells relative to the WL-grown cells, whereas content of competent PS I centers involved in photoinhibition of respiration remains almost the same in both the cultures. The effective antenna size of PS I was estimated to be 80-90 Chl d including 3-10 molecules absorbing at 735 nm. The effective optical cross-section of PS II corresponded to 90-100 Chl d and, presumably, 4 Chl a + 2 Pheo a [Mimuro et al. (1999) Biochim Biophys Acta 1412: 37-46]. Optical cross-section measurements indicated that the functional PS II units of A. marina attach one rod of four hexameric units of biliproteins.
Journal Article↗
Light control of Arabidopsis development entails coordinated regulation of genome expression and cellular pathways.
An expressed sequence tag-based microarray was used to profile genome expression underlying light control of Arabidopsis development. Qualitatively similar gene expression profiles were observed among seedlings grown in different light qualities, including far-red, red, and blue light, which are mediated primarily by phytochrome A, phytochrome B, and the cryptochromes, respectively. Furthermore, light/dark transitions also triggered similar differential genome expression profiles. Most light treatments also resulted in distinct expression profiles in small fractions of the expressed sequence tags examined. The similarly regulated genes in all light conditions were estimated to account for approximately one-third of the genome, with three-fifths upregulated and two-fifths downregulated by light. Analysis of those light-regulated genes revealed more than 26 cellular pathways that are regulated coordinately by light. Thus, light controls Arabidopsis development through coordinately regulating metabolic and regulatory pathways.
Arabidopsis↗
Spectral quality affects disease development of three pathogens on hydroponically grown plants.
Plants were grown under light-emitting diode (LED) arrays with various spectra to determine the effects of light quality on the development of diseases caused by tomato mosaic virus (ToMV) on pepper (Capsicum annuum L.), powdery mildew [Sphaerotheca fuliginea (Schlectend:Fr.) Pollaci] on cucumber (Cucumis sativus L.), and bacterial wilt (Pseudomonas solanacearum Smith) on tomato (Lycopersicon esculentum Mill.). One LED (660) array supplied 99% red light at 660 nm (25 nm bandwidth at half-peak height) and 1% far-red light between 700 to 800 nm. A second LED (660/735) array supplied 83% red light at 660 nm and 17% far-red light at 735 nm (25 nm bandwidth at half-peak height). A third LED (660/BF) array supplied 98% red light at 660 nm, 1% blue light (BF) between 350 to 550 nm, and 1% far-red light between 700 to 800 nm. Control plants were grown under broad-spectrum metal halide (MH) lamps. Plants were grown at a mean photon flux (300 to 800 nm) of 330 micromoles m-2 s-1 under a 12-h day/night photoperiod. Spectral quality affected each pathosystem differently. In the ToMV/pepper pathosystem, disease symptoms developed slower and were less severe in plants grown under light sources that contained blue and UV-A wavelengths (MH and 660/BF treatments) compared to plants grown under light sources that lacked blue and UV-A wavelengths (660 and 660/735 LED arrays). In contrast, the number of colonies per leaf was highest and the mean colony diameters of S. fuliginea on cucumber plants were largest on leaves grown under the MH lamp (highest amount of blue and UV-A light) and least on leaves grown under the 660 LED array (no blue or UV-A light). The addition of far-red irradiation to the primary light source in the 660/735 LED array increased the colony counts per leaf in the S. fuliginea/cucumber pathosystem compared to the red-only (660) LED array. In the P. solanacearum/tomato pathosystem, disease symptoms were less severe in plants grown under the 660 LED array, but the effects of spectral quality on disease development when other wavelengths were included in the light source (MH-, 660/BF-, and 660/735-grown plants) were equivocal. These results demonstrate that spectral quality may be useful as a component of an integrated pest management program for future space-based controlled ecological life support systems.
Biomass↗
Interactions of phytochromes A, B1 and B2 in light-induced competence for adventitious shoot formation in hypocotyl of tomato (Solanum lycopersicum L.).
The interactions of phytochrome A (phyA), phytochrome B1 (phyB1) and phytochrome B2 (phyB2) in light-dependent shoot regeneration from the hypocotyl of tomato was analysed using all eight possible homozygous allelic combinations of the null mutants. The donor plants were pre-grown either in the dark or under red or far-red light for 8 days after sowing; thereafter hypocotyl segments (apical, middle and basal portions) were transferred onto hormone-free medium for culture under different light qualities. Etiolated apical segments cultured in vitro under white light showed a very high frequency of regeneration for all of the genotypes tested besides phyB1phyB2, phyAphyB1 and phyAphyB1phyB2 mutants. Evidence is provided of a specific interference of phyB2 with phyA-mediated HIR to far-red and blue light in etiolated explants. Pre-treatment of donor plants by growth under red light enhanced the competence of phyB1phyB2, phyAphyB1 and phyAphyB1phyB2 mutants for shoot regeneration, whereas pre-irradiation with far-red light enhanced the frequency of regeneration only in the phyAphyB1 mutant. Multiple phytochromes are involved in red light- and far-red light-dependent acquisition of competence for shoot regeneration. The position of the segments along the hypocotyl influenced the role of the various phytochromes and the interactions between them. The culture of competent hypocotyl segments under red, far-red or blue light reduced the frequency of explants forming shoots compared to those cultured under white light, with different genotypes having different response patterns.
Genes, Plant↗
The cyanobacterial phytochrome Cph2 inhibits phototaxis towards blue light.
We analysed the effects of inactivation of the phytochrome genes cph1 and cph2 on the phototactic migration of the cyanobacterium Synechocystis sp. PCC 6803 under different light qualities. Motility towards white, green, red and far red light was not altered in several independently raised cph1, cph2 and cph1/cph2 double mutants. Blue light (lambda = 400-500 nm) did not induce motility in wild-type and cph1 mutant cells, whereas cph2 and cph1/cph2 double mutants moved towards the blue light. Inhibition of the photosynthetic electron transport by DCMU influenced the motility of cph2 mutants under blue light, but not under white, red and far red light. RNA blot hybridizations did not indicate an altered transcript accumulation of the pilin-encoding pilA1 gene under blue light. We propose that the Cph2 protein is part of a light-stimulated signal transduction chain inhibiting the movement of Synechocystis sp. PCC 6803 cells towards blue light.
Bacterial Proteins↗
Control of the Photosynthetic Apparatus of Acetabularia mediterranea by Blue Light : Analysis by Light-Saturation Curves.
During growth, Acetabularia mediterranea requires the action of blue light to maintain high rates of photosynthesis. In the present study, blue light-dependent alterations of the photosynthetic apparatus, which can be detected by analysis of light-saturation curves and by measurements of partial reactions of the photosynthetic electron transport chain, are described. Light-saturation curves of photosynthesis in vivo were measured with a new closed oxygen electrode system after culture of Acetabularia in continuous red or blue light. These curves were compared to those of 2,6-dichlorophenol-indophenol reduction by isolated chloroplast membranes. The analysis lead to the following statements: (a) only one reaction limits electron transport rates in vitro (dichlorophenol-indophenol reduction) at all light intensities irrespective of the light quality during growth, and (b) the limiting step is light driven and located in the reaction center of photosystem II. Presumably, this same reaction determines the flow of electrons under low light intensities in vivo in cells from white, blue, and red light. In addition to photosynthesis, the rates of dark respiration changed due to the action of blue light. Concomitantly, the light compensation point of apparent photosynthesis was shifted during monochromatic irradiations.
Journal Article↗
Phototherapy of acne vulgaris with visible light.
BACKGROUND: Sun exposure has a beneficial effect on acne vulgaris, but it is not clear which wavelengths contribute to the favourable effect. OBJECTIVE: The aim of the study was to investigate the effect of visible light on acne vulgaris and define the most effective wavelengths. METHODS: Thirty patients (15 men and 15 women) with mild to moderate acne vulgaris, involving the face and/or the back and/or the chest, were treated with three different light sources. They were treated 3 times a week, for a total of 7 weeks, each field for 20 min per session. RESULTS: All the light sources using 'full spectrum', green and violet improved the acne, leading to 14% (p > 0.10), 22% (p < 0.05) and 30% (p < 0.02) improvement, respectively. No statistically significant differences between the three different light sources were found, although there was a tendency that violet light was better than the other light qualities. No side-effects were observed. CONCLUSION: Visible light is a moderately effective alternative for treatment of acne vulgaris.
Acne Vulgaris↗
Light-curing renaissance makes materials popular. Technological upgrades boost quality in light-curing devices.
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Composite Resins↗
[Effect of light on the development of Saccobolus platensis].
The ascomycetous fungi Saccobolus platensis requires light for apothecial production. Photoinduction could be accomplished by continuous light and also by minor light periods. When apothecia were photoinduced by single 24 hour photoperiods, the effect varied according to the stage of development of the mycelium: it was most photoreceptive at the 5th day of growth. At this stage a single 6 hour irradiation was enough to induce 50% fructifications of the control (continuous light). After photoinduction, protoapothecia reached maturity independently of light treatment. Light quality influenced both apothecial number and size. Near ultraviolet light was the most effective for the induction of apothecia, followed by blue light; the maximum apothecial size was reached under blue light.
Ascomycota↗
Influence of light intensity, spectrum and orientation on sea bass plasma and ocular melatonin.
Melatonin is involved in the transduction of light information and the photoperiodic control of many important physiological functions in fish. Although artificial photoperiods have been used to improve fish growth and manipulate reproduction, there is little information about the characteristics of light 'quality'. In this paper we describe the effects of a light pulse in the middle of the dark phase on plasma and ocular melatonin in European sea bass. We first determined the light intensity necessary to elicit a melatonin response using white light of varying intensities (0.6-600 mu W/cm(2), experiment 1). Secondly, we tested the effect of the light spectrum on melatonin production using three differently coloured lights (half-peak bandwidth=434-477, 498-575 and 610-687 nm for the blue, green and red lamp, respectively, experiment 2) and, finally, we determined the effect of light orientation (downwards directed versus upwards directed, experiment 3). The results show that the minimum light intensity needed to inhibit or stimulate melatonin levels in both plasma and the eye was 6.0 mu W/cm(2). A linear correlation was found between the logarithm of light intensity and the relative inhibition. In addition, the blue wavelength was more effective in decreasing melatonin levels in the former and increasing the levels in the latter. Nevertheless, red light at sufficient intensity proved effective at significantly suppressing circulating melatonin. Downwards light had a greater effect than upward-directed illumination in suppressing plasma melatonin. In conclusion, the results point to the importance of giving proper consideration to the characteristics of light, to adequately control melatonin production and its related physiological processes.
Animals↗
Ethylene and auxin control the Arabidopsis response to decreased light intensity.
Morphological responses of plants to shading have long been studied as a function of light quality, in particular the ratio of red to far red light that affects phytochrome activity. However, changes in light quantity are also expected to be important for the shading response because plants have to adapt to the reduction in overall energy input. Here, we present data on the involvement of auxin and ethylene in the response to low light intensities. Decreased light intensities coincided with increased ethylene production in Arabidopsis rosettes. This response was rapid because the plants reacted within minutes. In addition, ethylene- and auxin-insensitive mutants are impaired in their reaction to shading, which is reflected by a defect in leaf elevation and an aberrant leaf biomass allocation. On the molecular level, several auxin-inducible genes are up-regulated in wild-type Arabidopsis in response to a reduction in light intensity, including the primary auxin response gene IAA3 and a protein with similarity to AUX22 and the 1-aminocyclopropane-1-carboxylic acid synthase genes ACS6, ACS8, and ACS9 that are involved in ethylene biosynthesis. Taken together, the data show that ethylene and auxin signaling are required for the response to low light intensities.
Arabidopsis↗
Green light stimulates early stem elongation, antagonizing light-mediated growth inhibition.
During the transition from darkness to light, the rate of hypocotyl elongation is determined from the integration of light signals sensed through the phototropin, cryptochrome, and phytochrome signaling pathways. In all light conditions studied, from UV to far-red, early hypocotyl growth is rapidly and robustly suppressed within minutes of illumination in a manner dependent upon light quality and quantity. In this study, it is shown that green light (GL) irradiation leads to a rapid increase in the growth rate of etiolated Arabidopsis seedlings. GL-mediated growth promotion was detected in response to constant irradiation or a short, single pulse of light with a similar time course. The response has a threshold between 10(-1) and 10(0) micromol m(-2), is saturated before 10(2) micromol m(-2) and obeys reciprocity. Genetic analyses indicate that the cryptochrome or phototropin photoreceptors do not participate in the response. The major phytochrome receptors influence the normal amplitude and timing of the GL response, yet the GL response is normal in seedlings grown for hours under constant dim-red light. Therefore, phytochrome activation enhances, but is not required for, the GL response. Seedlings grown under green, red, and blue light together are longer than those grown under red and blue alone. These data indicate that a novel GL-activated light sensor promotes early stem elongation that antagonizes growth inhibition.
Arabidopsis↗
Photomorphogenic responses in maize seedling development.
As an emerging maize (Zea mays) seedling senses light, there is a decrease in the rate of mesocotyl elongation, an induction of root growth, and an expansion of leaves. In leaf tissues, mesophyll and bundle sheath cell fate is determined, and the proplastids of each differentiate into the dimorphic chloroplasts typical of each cell type. Although it has been inferred from recent studies in several model plant species that multiple photoreceptor systems mediate this process, surprisingly little is known of light signal transduction in maize. Here, we examine two photomorphogenic responses in maize: inhibition of mesocotyl elongation and C4 photosynthetic differentiation. Through an extensive survey of white, red, far-red, and blue light responses among a diverse collection of germplasm, including a phytochrome-deficient mutant elm1, we show that light response is a highly variable trait in maize. Although all inbreds examined appear to have a functional phytochrome signal transduction pathway, several lines showed reduced sensitivity to blue light. A significant correlation was observed between light response and subpopulation, suggesting that light responsiveness may be a target of artificial selection. An examination of C4 gene expression patterns under various light regimes in the standard W22 inbred and elm1 indicate that cell-specific patterns of C4 gene expression are maintained in fully differentiated tissues independent of light quality. To our knowledge, these findings represent the first comprehensive survey of light response in maize and are discussed in relation to maize breeding strategies.
Base Sequence↗