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Different Light Intensities (different + light_intensity)
Selected AbstractsLoss of photic entrainment at low illuminances in rats with acute photoreceptor degenerationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 8 2009Domitille L. Boudard Abstract In several species, an acute injection of N -methyl- N -nitrosourea (MNU) induces a retinal degeneration characterized principally by a rapid loss of the outer nuclear layer, the other layers remaining structurally intact. It has, however, also been reported that down-regulation of melanopsin gene expression is associated with the degeneration and is detectable soon after injection. Melanopsin is expressed by a small subset of intrinsically photosensitive retinal ganglion cells and plays an important role in circadian behaviour photoentrainment. We injected MNU into Long Evans rats and investigated the ability of animals to entrain to three light/dark cycles of different light intensities (300, 15 and 1 lux). Control animals entrained their locomotor activity rhythms to the three cycles. In contrast, MNU-treated animals could only entrain properly to the 300 lux cycle. For the 15 lux cycle, their phase angle was much altered compared with control animals, and for the 1 lux cycle, MNU-injected animals were unable to photoentrain and exhibited an apparent free-run activity pattern with a period of 24.3 h. Subsequent to behavioural studies the animals were killed and rod, cone, melanopsin expression and melanopsin-expressing cells were quantified. Rod and cone loss was almost complete, melanopsin protein was reduced by 83% and melanopsin-expressing cells were reduced by 37%. Our study provides a comprehensive model of photoreceptor degeneration at the adult stage and a simple and versatile method to investigate the relation between retinal photoreceptors and the circadian system. [source] Regulation of Light Energy Utilization and Distribution of Photosynthesis in Five Subtropical Woody PlantsJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 3 2007Nan Liu Abstract The adaptations and responses of photosynthesis to long- and short-term growth light gradient treatments were investigated in five subtropical forest plants, namely Pinus massoniana Lamb., Schima superba Gardn. et Champ., Castanopsis fissa (Champ. ex Benth.) Rehd. et Wils., Acmena acuminatissima (BI.) Merr et Perry, and Cryptocarya concinna Hance. With diurnal changes in sunlight and air temperature, the de-epoxidation state and lutein content in the five woody plants under three light intensities first increased and then decreased during the day. However, maximal photochemical efficiency (Fv/Fm; where Fm is the maximum fluorescence yield and Fv is variable fluorescence) and the photochemical quantum yields of photosystem (PS) II (,PSII) of the species examined changed in the opposite manner, with those in plants grown under 100% natural light changing the most. After long-term treatment (21 months), anti-oxidant capacity (1, 1-diphenyl-2-picrylhydrazyl radical (DPPH·)-scavenging capacity) and utilization of excitation energy showed differences in modulation by different light intensities. It was shown that A. acuminatissima and C. concinna, as dominant species in the late succession stage of a subtropical forest in Dinghu mountain, South China, were better able to adapt to different light environments. However, P. massoniana, the pioneer species of this forest, exhibited less adaptation to low light intensity and was definitely eliminated by the forest succession process. [source] Importance of AOX pathway in optimizing photosynthesis under high light stress: role of pyruvate and malate in activating AOXPHYSIOLOGIA PLANTARUM, Issue 1 2010Challabathula Dinakar The present study shows the importance of alternative oxidase (AOX) pathway in optimizing photosynthesis under high light (HL). The responses of photosynthesis and respiration were monitored as O2 evolution and O2 uptake in mesophyll protoplasts of pea pre-incubated under different light intensities. Under HL (3000 µmol m,2 s,1), mesophyll protoplasts showed remarkable decrease in the rates of NaHCO3 -dependent O2 evolution (indicator of photosynthetic carbon assimilation), while decrease in the rates of respiratory O2 uptake were marginal. While the capacity of AOX pathway increased significantly by two fold under HL, the capacity of cytochrome oxidase (COX) pathway decreased by >50% compared with capacities under darkness and normal light (NL). Further, the total cellular levels of pyruvate and malate, which are assimilatory products of active photosynthesis and stimulators of AOX activity, were increased remarkably parallel to the increase in AOX protein under HL. Upon restriction of AOX pathway using salicylhydroxamic acid (SHAM), the observed decrease in NaHCO3 -dependent O2 evolution or p -benzoquinone (BQ)-dependent O2 evolution [indicator of photosystem II (PSII) activity] and the increase in total cellular levels of pyruvate and malate were further aggravated/promoted under HL. The significance of raised malate and pyruvate levels in activation of AOX protein/AOX pathway, which in turn play an important role in dissipating excess chloroplastic reducing equivalents and sustenance of photosynthetic carbon assimilation to balance the effects of HL stress on photosynthesis, was depicted as a model. [source] Effects of growth and measurement light intensities on temperature dependence of CO2 assimilation rate in tobacco leavesPLANT CELL & ENVIRONMENT, Issue 3 2010WATARU YAMORI ABSTRACT Effects of growth light intensity on the temperature dependence of CO2 assimilation rate were studied in tobacco (Nicotiana tabacum) because growth light intensity alters nitrogen allocation between photosynthetic components. Leaf nitrogen, ribulose 1·5-bisphosphate carboxylase/oxygenase (Rubisco) and cytochrome f (cyt f) contents increased with increasing growth light intensity, but the cyt f/Rubisco ratio was unaltered. Mesophyll conductance to CO2 diffusion (gm) measured with carbon isotope discrimination increased with growth light intensity but not with measuring light intensity. The responses of CO2 assimilation rate to chloroplast CO2 concentration (Cc) at different light intensities and temperatures were used to estimate the maximum carboxylation rate of Rubisco (Vcmax) and the chloroplast electron transport rate (J). Maximum electron transport rates were linearly related to cyt f content at any given temperature (e.g. 115 and 179 µmol electrons mol,1 cyt f s,1 at 25 and 40 °C, respectively). The chloroplast CO2 concentration (Ctrans) at which the transition from RuBP carboxylation to RuBP regeneration limitation occurred increased with leaf temperature and was independent of growth light intensity, consistent with the constant ratio of cyt f/Rubisco. In tobacco, CO2 assimilation rate at 380 µmol mol,1 CO2 concentration and high light was limited by RuBP carboxylation above 32 °C and by RuBP regeneration below 32 °C. [source] Strategies providing success in a variable habitat: II.PLANT CELL & ENVIRONMENT, Issue 10 2000Ecophysiology of photosynthesis of Cladophora glomerata ABSTRACT Cladophora glomerata (L.) Kütz. is the dominant filamentous algae of the river Ilm, Thuringia, Germany. For most of the year it can be found at open as well as at shaded sites. Photosynthetic acclimation of C. glomerata to different light intensities was detected by chlorophyll fluorescence measurements and pigment analysis. Cladophora glomerata from highlight sites showed decreased values of efficiency of open photosystem II (Fv/Fm) as compared with C. glomerata from low-light sites. Winter populations revealed higher Fv/Fm values than summer populations. A light-induced decrease in efficiency of the closed photosystem II was observed at increasing irradiance intensities. The decrease was higher in C. glomerata from shaded sites compared with plants from open sites. Differences in the photosynthetic electron transport rate of different populations of C. glomerata were shown by photosynthesis,irradiance curves. Summer populations from high-light sites yielded higher maximum electron transport rates than plants from low-light sites, whereas winter populations exhibited significantly decreased values compared with the summer populations. Results of the analysis of photosynthetic pigments corresponded with data from chlorophyll fluorescence measurements. In addition to these long-term acclimation effects, C. glomerata expressed its ability to cope with rapid changes in the light environment by the de-epoxidation of violaxanthin during exposure to high light intensities. [source] Series resistance characterization of industrial silicon solar cells with screen-printed contacts using hotmelt pastePROGRESS IN PHOTOVOLTAICS: RESEARCH & APPLICATIONS, Issue 6 2007A. Mette Abstract This work presents the results of a detailed series resistance characterization of silicon solar cells with screen-printed front contacts using hotmelt silver paste. Applying the hotmelt technology energy conversion efficiencies up to 18·0% on monocrystalline wafers with a size of 12·5,cm,×,12·5,cm have been achieved, an increase of 0·3% absolute compared to cells with conventional screen-printed contacts. This is mainly due to the reduction in the finger resistance to values as low as 14,,/m, which reduces the series resistance of the solar cell significantly. To retrieve the lumped series resistance as accurately as possible under the operating condition, different determination methods have been analyzed. Methods under consideration were fitting of the two-diode equation function to a dark IV-curve, integration of the area A under an IV-curve, comparison of a jsc,Voc with a one-sun IV-curve, comparison of the jsc and Voc points of a shaded curve with the one-sun IV-curve as well as comparison of a dark IV-curve with a one-sun IV-curve, and comparison of IV-curves measured at different light intensities. The performed investigations have shown that the latter four methods all resulted in reliable series resistance values. Copyright © 2007 John Wiley & Sons, Ltd. [source] Developmental and light effects on the accumulation of FtsH protease in Arabidopsis chloroplasts , implications for thylakoid formation and photosystem II maintenanceTHE PLANT JOURNAL, Issue 5 2005Adi Zaltsman Summary The chloroplast ATP-dependent metalloprotease FtsH is involved in the degradation of unassembled proteins, the repair of photosystem II (PSII) from photoinhibition, and, apparently, the formation of thylakoids. In Arabidopsis, it is encoded by a family of 12 genes. However, the products of only four of them, FtsH1, 2, 5 and 8, have been found in chloroplasts to date. Mutations in two of these, FtsH2 and 5, demonstrate a visible phenotype of variegated leaves, with the phenotype of the FtsH2 mutant being more pronounced. Moreover, the degree of variegation appears to be dependent on developmental stage and environmental factors, suggesting an intricate relationship between the different gene products. To explore this, developmental and light effects on the accumulation of FtsH protease were studied in wild-type (WT) and FtsH2-mutant plants. Whereas cotyledons of the mutant were indistinguishable from those of the WT, the first true leaves were almost completely white. Subsequent leaves contained increasing proportions of green sectors. Analysis of the mRNA of the four FtsH genes, in cotyledons, first and second leaves of WT and mutant plants, revealed that: (i) transcript level increases during development, and (ii) transcript level in the mutant is higher than in the WT. FtsH protein level in the mutant was ca. 50% of that found in the WT, whereas the levels of other thylakoid proteins were the same. In individual leaves, the level of FtsH protein increased during development as well. Exposure of seedlings to different light intensities did not affect the degree of variegation, suggesting that it is due to a defect in chloroplast development rather than photobleaching. Examination of FtsH protein during exposure to high light revealed a decrease in its level, concomitant with a decrease in PSII potential, suggesting that the kinetics of photoinhibition reflects not only photodamage to PSII and induction of protective mechanisms, but also a decrease in repair capacity due to a reduction in the level of FtsH protease. [source] | ||||||||||