Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “light quality”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
PubMed1997

Changes in photosystem stoichiometry in response to environmental conditions for cell growth observed with the cyanophyte Synechocystis PCC 6714.

Changes in photosystem stoichiometry in response to shift of environments for cell growth other than light regime were studied with the cyanophyte Synechocystis PCC 6714 in relation to the change induced by light-quality shift. Following two environment-shifts were examined: the shift of molecular form of inorganic carbon source for photosynthesis from CO2 to HCO3- (CO2 stress) and the increase in salinity of the medium with NaCl (0.5 M) (Na+ stress). Both CO2 and Na+ stresses induced the increase in PSI abundance resulting in a higher PSI/PSII stoichiometry. CO2 stress was found to elevate simultaneously Cyt c oxidase activity (Vmax). The feature was the same as that caused by light-quality shift from preferential excitation of PSI to PSII (light stress) though the enhancement by either stress was smaller than that by light stress. Under our experimental conditions, PSI/PSII stoichiometry appeared to increase at a fairly constant rate to the basal level even when the basal level had been differently determined by the light-quality. Enhancing rates for PSI/PSII stoichiometry and for Cyt c oxidase activity were also similar to each other. Since the two stresses affect the thylakoid electron transport similarly to the shift of light-quality, we interpreted our results as follows: three environmental stresses, CO2, Na+, and light stresses, cause changes in electron turnover capacity of PSI and Cyt c oxidase under a similar, probably a common, mechanism for monitoring redox state of thylakoid electron transport system.

Carbon Dioxide↗
PubMed2025

Multi-Omics Analyses Reveal the Red and Far-Red Light Combination Enhancing Heterologous Protein and Metabolite Production in Nicotiana benthamiana.

Transient expression of exogenous protein in Nicotiana benthamiana leaves via agroinfiltration offers a rapid and efficient platform for functional gene discovery and heterologous production of valuable eukaryotic proteins and metabolites. Though light quality is an important factor for plant photomorphogenesis, its impact on the efficiency of transient expression remains unexplored. In this study, we examined the influence of five representative light qualities with varying wavelength mix on the N. benthamiana growth and recombinant green fluorescent protein (GFP) production. Plants with red and far-red light treatment (LED-red) showed the highest GFP expression, 57.4% higher than white light. Further study showed that a higher dosage of post-infiltration Agrobacterium and the resulting increase in the number of transcripts contribute to the expression rate enhancement. Moreover, as for exogenous metabolites, a 76.5% increase of accumulated taxadiene was also observed in LED-red group. Integrated transcriptomic, proteomic and metabolomic revealed that LED-red plants reduced the resistance pathways before infiltration, inducing a higher dosage of post-agroinfiltration Agrobacterium. Our results suggest that N. benthamiana grown under LED-red creates a more favorable environment for Agrobacterium growth, enhancing heterologous protein and metabolite production. This study highlights the potential utilization of light quality as an implementable tool in plant synthetic biology.

Nicotiana↗
PubMed2000

Light and adaptive responses in red macroalgae: an overview.

The most recent research shows an increased interest in algal photobiology following the modifications of light spectral composition induced by the 'ozone depletion' in the atmosphere. The consequences of this change on the macrophytic red algae, which possess accessory light-harvesting complexes, are currently uncertain. Moreover the underwater light field of coastal waters, where most macroalgae are living, has been well characterized only in the last few years. The presence and the variability of light components, such as red, far-red, green, blue and ultraviolet radiation, in these environments, at different depths, have raised the question of whether red macroalgae are 'light-intensity or/and light-quality adapters'. In this paper various adaptive responses of red algae, both in the field and under culture, are discussed in order to compare the physiological and ecological results. All these studies seem to suggest that red algae are both 'light-intensity and light-quality adapters'. In particular, the light quality and, overall, the modulation of the ratios between spectral components seem to play the role of photomorphogenic 'signals' regulating algal metabolism and growth. Short- and long-term responses, and potential strategies and mechanisms for adaptation to light at individual, cellular and molecular levels, are discussed with special reference to the photosynthetic equipment.

Adaptation, Physiological↗
PubMed2002

A turquoise mutant genetically separates expression of genes encoding phycoerythrin and its associated linker peptides.

During complementary chromatic adaptation (CCA), cyanobacterial light harvesting structures called phycobilisomes are restructured in response to ambient light quality shifts. Transcription of genes encoding components of the phycobilisome is differentially regulated during this process: red light activates cpcB2A2, whereas green light coordinately activates the cpeCDE and cpeBA operons. Three signal transduction components that regulate CCA have been isolated to date: a sensor-photoreceptor (RcaE) and two response regulators (RcaF and RcaC). Mutations in the genes encoding these components affect the accumulation of both cpcB2A2 and cpeBA gene products. We have isolated and characterized a new pigmentation mutant called Turquoise 1. We demonstrate that this mutant phenotype is due to a dramatic decrease in cpeBA transcript abundance and results from a lesion in the cpeR gene. However, in this mutant cpeCDE RNA levels remain near those found in wild-type cells. Our results show that the coordinate regulation of cpeBA and cpeCDE by green light can be uncoupled by the loss of CpeR, and we furnish the first genetic evidence that different regulatory mechanisms control these two operons. Sequence analysis of CpeR reveals that it shares limited sequence similarity to members of the PP2C class of protein serine/threonine phosphatases. We also demonstrate that cpeBA and cpeCDE retain light quality responsiveness in a mutant lacking the RcaE photoreceptor. This provides compelling evidence for the partial control of CCA through an as-yet-uncharacterized second light quality sensing system.

Amino Acid Sequence↗
PubMed2000

Plasticity versus canalization: population differences in the timing of shade-avoidance responses.

The reliability of environmental cues and costs of a fixed phenotype are two factors determining whether selection favors phenotypic plasticity or environmental specialization. This study examines the relationship between these two factors and the evolution of plant competitive strategies (plastic vs. fixed morphologies). In natural plant populations, shifts in light quality associated with foliar shade reliably indicate the presence of neighbors. These cues mediate plastic stem-elongation responses that often increase competitive ability and access to light. Using experimental light treatments (full sun, neutral shade, and foliar shade), genetic differences among populations of Abutilon theophrasti (velvetleaf) in average elongation and plasticity to foliar-shade cues were examined. Six populations, two from each of three site types (fields in continuous corn cultivation, fields undergoing corn-soy rotation, and weedy sites), were exposed to the light treatments at two stages in their life history. At the seedling stage, populations derived from cornfield sites exhibited higher, average elongation than populations from either rotating corn-soy fields or weedy areas. Because seedling elongation may delay shading of velvetleaf by corn, population differences may reflect adaptive responses to directional selection imposed by competitive conditions. However, the effects of simulated foliar shade on elongation were three times as great as the average population differences, and these comparatively higher levels of elongation were associated with an allocation cost. These results are consistent with the hypothesis that phenotypic plasticity may limit the evolution of specialists; reliable environmental cues enable individuals to facultatively adopt highly elongated, costly phenotypes in crowded patches while avoiding the costs of that phenotype in less crowded microsites. At later life-history stages, populations experiencing competition with corn exhibited lower plasticity to light quality than populations derived from weedy areas. Elongation at later nodes is maladaptive in cornfields because velvetleaf is ultimately incapable of overtopping corn; individuals that elongate therefore experience the cost of allocating to stems but fail to improve leaf exposure. The decreased responsiveness of cornfield populations to light quality is consistent with theoretical predictions in which reduced plasticity is favored when environmental cues fail to mediate an adaptive response.

Biological Evolution↗
PubMed2006

Melatonin in Glycyrrhiza uralensis: response of plant roots to spectral quality of light and UV-B radiation.

Melatonin (N-acetyl-5-methoxytryptamine) is known to be synthesized and secreted by the pineal gland in vertebrates. Evidence for the occurrence of melatonin in the roots of Glycyrrhiza uralensis plants and the response of this plant to the spectral quality of light including red, blue and white light (control) and UV-B radiation (280-315 nm) for the synthesis of melatonin were investigated. Melatonin was extracted and quantified in seed, root, leaf and stem tissues and results revealed that the root tissues contained the highest concentration of melatonin; melatonin concentrations also increased with plant development. After 3 months of growth under red, blue and white fluorescent lamps, the melatonin concentrations were highest in red light exposed plants and varied depending on the wavelength of light spectrum in the following order red >> blue > or = white light. Interestingly, in a more mature plant (6 months) melatonin concentration was increased considerably; the increments in concentration were X4, X5 and X3 in 6-month-old red, blue and white light exposed (control) plants, respectively. The difference in melatonin concentrations between blue and white light exposed (control) plants was not significant. The concentration of melatonin quantified in the root tissues was highest in the plants exposed to high intensity UV-B radiation for 3 days followed by low intensity UV-B radiation for 15 days. The reduction of melatonin under longer periods of UV-B exposure indicates that melatonin synthesis may be related to the integrated (intensity and duration) value of UV-B irradiation. Melatonin in G. uralensis plant is presumably for protection against oxidative damage caused as a response to UV irradiation.

Glycyrrhiza uralensis↗
PubMed2005

Light sources with different spectra affect root and mycorrhiza formation in Scots pine in vitro.

We studied the effects of broad-spectrum light quality on the interaction between the ectomycorrhizal fungus Pisolithus tinctorius (Pers.) Coker and Couch and Scots pine (Pinus sylvestris L.) seedlings and hypocotyl cuttings cultured in vitro. The light sources were cool white (CW), warm white (WW) and red-rich daylight (RD) fluorescent lamps. Inoculation with P. tinctorius enhanced adventitious root formation of the cuttings in all light treatments. Rooting of the inoculated cuttings was highest in WW light (89%), followed by CW (73%) and RD light (66%). During 6 weeks of in vitro culture, rooted cuttings formed only a few lateral roots. The fungus grew over lateral roots, but the Hartig net was absent in all light treatments. In non-inoculated cuttings, neither root formation nor subsequent root growth was affected by light quality. In the seedling experiment, inoculation in the WW treatment resulted in a significantly (P < 0.05) greater number of lateral roots than inoculation in the RD treatment. The percentage of lateral roots covered with fungal hyphae was also highest in WW light (62%), followed by CW (50%) and RD (27%) light. A similar pattern was observed in the intensity of Hartig net formation. We conclude that effects of broad-spectrum light quality on the ectomycorrhizal fungus-root interaction are dependent on the developmental stage of the root.

Basidiomycota↗
PubMed2002

Effects of UV and visible light on cyanobacteria at the cellular level.

The effect of UV and visible light on cyanobacteria was determined at the cellular level by means of epifluorescence and confocal microscopy techniques. These methods allow the examination of light effects in spatial resolution. Series of measurements were performed to determine the effect of different light qualities and quantities on cyanobacteria. To analyze the effect of the light quality, samples of Anabaena and Scytonema sp. were exposed to intense blue, green or red light applied from the epifluorescence path of the microscope. The fluorescence of the phycobiliproteins was recorded by means of epifluorescence (excitation 550 nm, 20 nm half band width (HBW), emission above 635 nm) or by confocal microscopy (560 nm laser line). Upon exposure to blue or green light the cells showed an increase in fluorescence followed by a sudden and complete loss of fluorescence. Blue light was more effective (bleaching of phycobiliproteins within 45 min) than green light (bleaching within 120 min). Red light was not as effective, and bleaching of the cells took at least 24 h. Initially the cells showed an increase in fluorescence followed by fast bleaching of the fluorescence signal. Cells exposed to UV plus PAR were bleached within 60 min, while cells exposed to photosynthetically active radiation (PAR) only were totally bleached after about 120 min. FL-DHP (dihydropyridine) labeling was performed in two cyanobacteria, Anabaena sp. and Nostoc commune, to visualize L-type calcium channels. Both cyanobacterial strains showed a pronounced FL-DHP signal of the heterocysts and akinetes but only a weak signal from the vegetative cells. The results clearly indicate the presence of calcium channels in these cells. UV radiation decreased the amount of chlorophyll and phycocyanin as could be seen from a decline in the autofluorescence of the cells. In contrast, the FL-DHP signal was not affected by UV.

Cyanobacteria↗
PubMed2006

Comparative water quality of lightly- and moderately-impacted streams in the southern Blue Ridge Mountains, USA.

For less-developed regions like the Blue Ridge Mountains, data are limited that link basin-scale land use with stream quality. Two pairs of lightly-impacted (90-100% forested) and moderately-impacted (70-80% forested) sub-basins of the upper Little Tennessee River basin in the southern Blue Ridge were identified for comparison. The pairs contain physically similar stream reaches, chosen for the purpose of isolating forest conversion as a potential driver of any detected differences in water quality. Streams were sampled during baseflow conditions twice monthly over a six-month period from September 2003 through February 2004. Parametric t-tests were run for each parameter measured between the lightly-and moderately-impacted streams within each pair. Statistically significantly higher mean values of suspended and dissolved solids, nitrate, specific conductivity, turbidity, and temperature were observed in the moderately impacted streams versus the lightly impacted streams in both pairs, while dissolved oxygen levels were lower in the moderately-impacted streams. No significant differences were demonstrated in orthophosphate or ammonium concentration. A near-bankfull runoff event on February 6, 2004, was sampled for stormflow values, and the results support baseflow findings. The water quality of these streams is very good when compared with lower relief areas like the Piedmont, and none of the parameters measured in this study exceeds levels of known threat to stream biota. However, the demonstration that moderate reductions in forest cover are associated with stream water quality degradation carries important implications for stream management in this rapidly developing mountainous region.

Environmental Monitoring↗
PubMed2003

Effect of specific wavelengths on light-induced quality changes in Havarti cheese.

The effects of exposure of slices of Havarti cheeses to monochromatic light of wavelengths 366 nm, 405 nm, and 436 nm, respectively, were studied by tristimulus colorimetry, solid-phase microextraction gas chromatographic analysis of volatiles, and open-end fluorescence spectroscopy. Having determined the photon fluxes of the three wavelengths by ferrioxalate actinometry, it was possible to quantify the effects of light exposure in an absolute manner. For all analyses, the most severe effects were caused by visible light, leading to colour bleaching, change in hue, riboflavin degradation, and formation of the secondary oxidation products hexanal, 1-pentanol, and 1-hexanol. Apparent quantum yields for formation of hexanal and 1-pentanol were found to be insignificantly different for 405 nm and 436 nm exposures, having values of (3-5) x 10(-5) mol x einstein(-1) and (9-13) x 10(-5) mol x einstein(-1), respectively. These compounds were not formed when exposed to 366 nm light. In contrast, 1-hexanol was formed when exposing cheese to all three wavelengths, resulting in apparent quantum yields of (2-6) x 10(-5) mol x einstein(-1). The results obtained are discussed in relation to the interplay between inherent product colorants, light sources, and transmission characteristics of the packaging materials.

Aldehydes↗
PubMed1992

Stimulation of growth and ion uptake in bean leaves by red and blue light.

Red and blue light both stimulate growth and ion accumulation in bean (Phaseolus vulgaris L.) leaves, and previous studies showed that the growth response is mediated by phytochrome and a blue-light receptor. Results of this study confirm that there is an additional photosynthetic contribution from the growing cells that supports ion uptake and growth. Disc expansion in the light was enhanced by exogenous K(+) and Rb(+), but was not specific for anions. Light increased K(+) accumulation and the rate of (86)Rb(+) uptake by discs, over darkness, with no effect of light quality. The photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea, inhibited light-driven (86)Rb(+) uptake by 75%. Light quality caused differences in short-term kinetics of growth and acidification of the leaf surface. At comparable fluence rates (50 mumol m(-2) s(-1)), continuous exposure to blue light increased the growth rate 3-fold after a 2-min lag, whereas red light caused a smaller growth response after a lag of 12 min. In contrast, the acidification of the leaf surface normally associated with growth was stimulated 3-fold by red light but only slightly (1.3-fold) by blue light. This result shows that, in addition to acidification caused by red light, a second mechanism specifically stimulated by blue light is normally functioning in light-driven leaf growth.

Journal Article↗
PubMed2000

Nucleo-cytoplasmic partitioning of the plant photoreceptors phytochromes.

Phytochromes in harmony with blue light photoreceptors play a major role in controlling plant growth and development from germination to seed maturation. Light absorption by phytochromes triggers a signaling cascade, phototransduction, which culminates in regulated gene expression. A major regulatory step at the cellular level, which affects specificities of light-induced physiological responses, seems to be the light-quality and light-quantity dependent nuclear import of the phytochromes themselves. The correlations found between the nuclear import of phytochromes (phyA and phyB) and various physiological responses regulated by these photoreceptors provides strong support for this hypothesis.

Active Transport, Cell Nucleus↗
PubMed1986

Cyanobacterial Acclimation to Photosystem I or Photosystem II Light.

The organization and function of the photochemical apparatus of Synechococcus 6301 was investigated in cells grown under yellow and red light regimes. Broadband yellow illumination is absorbed preferentially by the phycobilisome (PBS) whereas red light is absorbed primarily by the chlorophyll (Chl) pigment beds. Since PBSs are associated exclusively with photosystem II (PSII) and most of the Chl with photosystem I (PSI), it follows that yellow and red light regimes will create an imbalance of light absorption by the two photosystems. The cause and effect relationship between light quality and photosystem stoichiometry in Synechococcus was investigated. Cells grown under red light compensated for the excitation imbalance by synthesis/assembly of more PBS-PSII complexes resulting in high PSII/PSI = 0.71 and high bilin/Chl = 1.30. The adjustment of the photosystem stoichiometry in red light-grown cells was necessary and sufficient to establish an overall balanced absorption of red light by PSII and PSI. Cells grown under yellow light compensated for this excitation imbalance by assembly of more PSI complexes, resulting in low PSII/PSI = 0.27 and low bilin/Chl = 0.42. This adjustment of the photosystem stoichiometry in yellow light-grown cells was necessary but not quite sufficient to balance the absorption of yellow light by the PBS and the Chl pigment beds. A novel excitation quenching process was identified in yellow light-grown cells which dissipated approximately 40% of the PBS excitation, thus preventing over-excitation of PSII under yellow light conditions. It is hypothesized that State transitions in O(2) evolving photosynthetic organisms may serve as the signal for change in the stoichiometry of photochemical complexes in response to light quality conditions.

Journal Article↗
PubMed2003

Role of chloroplast protein kinase Stt7 in LHCII phosphorylation and state transition in Chlamydomonas.

Photosynthetic organisms adapt to changes in light quality by redistributing light excitation energy between two photosystems through state transition. This reorganization of antenna systems leads to an enhanced photosynthetic yield. Using a genetic approach in Chlamydomonas reinhardtii to dissect the signal transduction pathway of state transition, we identified a chloroplast thylakoid-associated serine-threonine protein kinase, Stt7, that has homologs in land plants. Stt7 is required for the phosphorylation of the major light-harvesting protein (LHCII) and for state transition.

Algal Proteins↗
PubMed1992

Toxin Production by Microcystis aeruginosa as a Function of Light in Continuous Cultures and Its Ecological Significance.

The effects of light intensity and light quality on toxin production by Microcystis aeruginosa were examined in continuous cultures. Light intensity had a pronounced effect on toxicity and the toxin production rate. Toxicity and the toxin production rate increased with light intensity up to an intensity of about 40 microeinsteins m s and decreased at higher light intensities, while the ratio of toxin to protein was constant at intensities of more than 40 microeinsteins m s. Light quality had only slight effects on toxicity. The results of our laboratory experiments were supported by the results of field work in which we examined toxin production at different depths in a lake. Our observations explain the mixed pattern of high and low toxicity found in a surface bloom of M. aeruginosa. Our findings also indicate that production of the peptide toxin can be uncoupled from general protein synthesis.

Journal Article↗
PubMed2001

Intracellular trafficking of photoreceptors during light-induced signal transduction in plants.

Plants monitor changes in the ambient light environment by highly specialised photoreceptors, which include the red/far-red photoreversible phytochromes, the blue-light-absorbing cryptochromes and phototropin and the so-far-unidentified UVB photoreceptor(s). Light easily penetrates plant organs/tissues and reaches even the subcellular compartments of various cell types. Therefore, it is not surprising that the determination of the intracellular localisation of photoreceptors has been, for many years, a major, and often controversial, subject of plant photobiology and cell biology research. Phototropin, one of the blue-light photoreceptors of higher plants, controls phototropism by monitoring the direction of light, and it is localised in or at the plasmalemma. In contrast, the subcellular localisation of phytochromes changes dynamically and exhibits a very complex pattern. These photoreceptors are localised in the cytosol in dark- grown tissues. Irradiation, however, induces import of phytochromes into the nucleus. The import occurs in a light-quality- and light-quantity-dependent fashion and, as such, seems to be unique to higher plants. Light-induced accumulation of phytochromes in the nuclei correlates well with various physiological responses mediated by these photoreceptors. These observations indicate that light-dependent intracellular redistribution of phytochrome photoreceptors is one of the major regulatory steps in photomorphogenesis.

Darkness↗
PubMed1977

Occurrence and nature of chromatic adaptation in cyanobacteria.

Forty-four axenic strains of cyanobacteria that synthesize phycoerythrin were screened to ascertain the effect of light quality on pigment synthesis. Cellular pigment compositions were determined after photoautotrophic growth with low light fluxes (7.0 X 10(2) ergs/cm2 per s) of green, red, and white light, and in the case of facultative heterotrophs, after dark growth at the expense of sugars. Twelve strains did not adapt chromatically: the cells contained fixed proportions of phycoerythrin, phycocyanin, and allophycocyanin under the growth conditions used. In the remaining strains, the cellular ratio of phycoerythrin to phycocyanin was much higher after growth in green than in red light. Quantitative data on the cellular pigment contents, supplemented by measurements of the differential rates of pigment synthesis on representative strains, show that chromatic adaptation may involve a light-induced modulation either of phycoerythrin synthesis alone (7 strains) or of both phycoerythrin and phycocyanin synthesis (25 strains). Facultative hetrotrophs able to adapt chromatically have a phycobiliprotein composition after dark growth which closely resembles that after growth in red light. Light quality does not affect the differential rate of chlorophyll synthesis. The physiological and taxonomic implications of these findings are discussed.

Adaptation, Physiological↗
PubMed1995

Regulation of Early Light-Inducible Protein Gene Expression by Blue and Red Light in Etiolated Seedlings Involves Nuclear and Plastid Factors.

Early light-inducible proteins (ELIPs) are nuclear-encoded chloroplast proteins whose genes are transiently transcribed during the greening process of etiolated plants. In the present work the regulation of ELIP gene expression by blue and red light has been investigated in plumulas of etiolated pea plants (Pisum sativum). The results show that the steady-state level of ELIP transcripts is controlled by a combined action of phytochrome and blue light receptor systems and, in addition, depends on the age of the seedlings. Both a low-light fluence system of blue and a very-low-fluence system of red light are involved in ELIP induction. The threshold for accumulation of ELIP transcripts was as low as 10-5 [mu]E m-2 s-1 for both light qualities but a different pattern of accumulation was obtained in blue and in red light. Blue light not only acts at the level of transcription but also regulates the stability of the ELIP transcripts in a light intensity-dependent manner. Moreover, it is shown that product(s) of nuclear gene(s) negatively regulate the steady-state level of ELIP transcripts during the 1st h of illumination with red light. Preillumination of seedlings with white light abolishes this repression. Accumulation of ELIP transcripts requires "plastid factors" in both blue and red light qualities.

Journal Article↗