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Low Light Intensity (low + light_intensity)
Selected AbstractsThe Effect of Irradiance on Carboxylating/Decarboxylating Enzymes and Fumarase Activities in Mesembryanthemum crystallinum L. Exposed to Salinity StressPLANT BIOLOGY, Issue 1 2001Z. Miszalski Abstract: In Mesembryanthemum crystallinum plants, treated for 9 days with 0.4 M NaCl at low light intensities (80 - 90 or 95 - 100 ,E m -2 s -1; , = 400 - 700 nm), no day/night malate level differences (,malate) were detected. At high light (385 - 400 ,E m -2 s -1) strong stimulation of PEPC activity, accompanied by a ,malate of 11.3 mM, demonstrated the presence of CAM metabolism. This indicates that, to evolve day/night differences in malate concentration, high light is required. Salt treatment at low light induces and increases the activity of NAD- and NADP-malic enzymes by as much as 3.7- and 3.9-fold, while at high light these values reach 6.4- and 17.7-fold, respectively. The induction of activity of both malic enzymes and PEPC (phospoenolpyruvate carboxylase) take place before ,malate is detectable. An increase in SOD (superoxide dismutase) was observed in plants cultivated at high light in both control and salt-treated plants. However, in salt-treated plants this effect was more pronounced. Carboxylating and decarboxylating enzymes seem to be induced by a combination of different signals, i.e., salt and light intensity. Plants performing CAM, after the decrease of activity of both the decarboxylating enzymes at the beginning of the light period, showed an increase in these enzymes in darkness when the malate pool reaches higher levels. In CAM plants the activity of fumarase (Krebs cycle) is much lower than that in C3 plants. The role of mitochondria in CAM plants is discussed. [source] 3423: Measurement of straylightACTA OPHTHALMOLOGICA, Issue 2010HS GINIS Purpose Straylight in the human eye is associated with low light intensities scattered at angles large compared to the part of the Point Spread Function that is governed by refractive error and aberrations. It is the purpose of this talk to summarise existing methods for the measurement of straylight in the human eye and to discuss new developments. Methods Among psychophysical techniques are the most well-established and studied methods. Optical techniques to date are limited by signal to noise as well as dynamic range considerations. Results Improvements in optical techniques involve the creation of the appropriate imaging conditions where scattered light intensity can be calculated based on the effects of scatter on the acquired image. Conclusion Psychophysical methods, that have been particularly successful, require specially designed optical schemes (for the presentation of the stimulus), a specific task and a suitable data analysis method. Optical techniques may benefit from refinements in these directions also. [source] Response of Oryzacystatin I Transformed Tobacco Plants to Drought, Heat and Light StressJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2010K. Demirevska Abstract Transformed tobacco plants expressing a rice cysteine proteinase inhibitor (OC-I) and non-transformed plants were grown in a controlled environment and subjected to various stresses. Two-month-old transformed and non-transformed plants were exposed for 5 days to drought conditions by withholding watering. High temperature (40 °C) was applied additionally at day 6th for 5 h either individually or in combination with drought. All stress treatments were applied under low (150 ,mol m,2 s,1 PPFD) and high light intensity (HL) of 1000 ,mol m,2 s,1 PPFD to determine if OC-I expression might provide protection under combination of stresses usually existing in nature. Drought stress led to diminution in leaf relative water content, photosynthesis inhibition, decrease in chlorophyll content and accumulation of malondialdehyde and proline. Heat stress alone did not affect the plants significantly, but intensified the effect of drought stress. HL intensity further increased the proline content. OC-I transformed plants grown under low light intensity had significantly higher total superoxide dismutase and guaiacol peroxidase activities as well as their isoforms than non-transformed control plants under non-stress and stress conditions. Catalase activity was not highly affected by OC-I expression. Results indicate that OC-I expression in tobacco plants provides protection of the antioxidative enzymes superoxide dismutase and guaiacol peroxidise under both non-stress and stress conditions. [source] Allocation of Photosynthates and Grain Growth of Two Wheat Cultivars with Different Potential Grain Growth in Response to Pre- and Post-anthesis ShadingJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 5 2003Z. Wang Abstract Grain yield in wheat is dependent on photosynthate production and allocation. Light intensity is one of the main factors affecting photosynthate production and allocation, and grain yield. This study was conducted to determine whether cultivars varying in grain number per spike and grain weight respond differently to pre-anthesis shading (PRE) and post-anthesis shading (POST), and to characterize the responses in production and allocation of photosynthate, yield and yield components, and spike traits. Both PRE and POST caused a decrease in both dry matter (DM) accumulation and allocation to grain. Cultivar Lumai 22, which has a large spike and large grains, was more sensitive to either PRE or POST. PRE reduced photosynthate production and partitioning to the spike in Lumai 22 at anthesis. In contrast, PRE had little influence on these parameters in the small-spike, small-grain cultivar Yannong 15. POST reduced the partitioning to the grain, especially in Lumai 22, for which marked reductions in biomass and grain yield were found for both the PRE and POST treatments. Changes in yield components attributable to shading varied with cultivars. The number of spikes m,2 was not affected by either PRE or POST. Lumai 22 was more seriously affected by shading than Yannong 15 in terms of grain number per spike and weight per grain. The decreases in grain number or weight per spikelet in both the PRE and POST treatments took place mainly in the upper and basal spikelets, especially in Lumai 22. We concluded that the adaptability of the small-spike, small-grain cultivar Yannong 15 to either PRE or POST was much greater than that of the large-spike, large-grain cultivar Lumai 22 in terms of many characteristics closely related to grain yield. Hence, we suggest that, in areas where low light intensity often occurs, the small-spike, small-grain cultivar would be more likely to produce high, stable grain yields. [source] The Effect of Decreasing Temperature up to Chilling Values on the in vivo F685/F735 Chlorophyll Fluorescence Ratio in Phaseolus vulgaris and Pisum sativum: The Role of the Photosystem I Contribution to the 735 nm Fluorescence Band ,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2000Giovanni Agati ABSTRACT The effect of leaf temperature (T), between 23 and 4°C, on the chlorophyll (Chl) fluorescence spectral shape was investigated under moderate (200 ,E m,2 s,1) and low (30,35 ,E m,2 s,1) light intensities in Phaseolus vulgaris and Pisum sativum. With decreasing temperature, an increase in the fluorescence yield at both 685 and 735 nm was observed. A marked change occurred at the longer emission band resulting in a decrease in the Chl fluorescence ratio, F685/F735, with reducing T. Our fluorescence analysis suggests that this effect is due to a temperature-induced state 1,state 2 transition that decreases and increases photosystem II (PSII) and photosystem I (PSI) fluorescence, respectively. Time-resolved fluorescence lifetime measurements support this interpretation. At a critical temperature (about 6°C) and low light intensity a sudden decrease in fluorescence intensity was observed, with a larger effect at 685 than at 735 nm. This is probably linked to a modification of the thylakoid membranes, induced by chilling temperatures, which can alter the spillover from PSII to PSI. The contribution of photosystem I to the long-wavelength Chl fluorescence band (735 nm) at room temperature was estimated by both time-resolved fluorescence lifetime and fluorescence yield measurements at 685 and 735 nm. We found that PSI contributes to the 735 nm fluorescence for about 40, 10 and 35% at the minimal (F0), maximal (Fm) and steady-state (Fs) levels, respectively. Therefore, PSI must be taken into account in the analysis of Chl fluorescence parameters that include the 735 nm band and to interpret the changes in the Chl fluorescence ratio that can be induced by different agents. [source] Limitation of nocturnal import of ATP into Arabidopsis chloroplasts leads to photooxidative damage,THE PLANT JOURNAL, Issue 2 2007Thomas Reinhold Summary When grown in short day conditions and at low light, leaves of Arabidopsis plants with mutations in the genes encoding two plastidial ATP/ADP transporters (so-called null mutants) spontaneously develop necrotic lesions. Under these conditions, the mutants also display light-induced accumulation of H2O2 and constitutive expression of genes for copper/zinc superoxide dismutase 2 and ascorbate peroxidase 1. In the light phase, null mutants accumulate high levels of phototoxic protoporphyrin IX but have only slightly reduced levels of Mg protoporphyrin IX. The physiological changes are associated with reduced magnesium,chelatase activity. Since the expression of genes encoding any of the three subunits of magnesium,chelatase is similar in wild type and null mutants, decreased enzyme activity is probably due to post-translational modification which might be due to limited availability of ATP in plastids during the night. Surprisingly, the formation of necrotic lesions was absent when null mutants were grown either in long days and low light intensity or in short days and high light intensity. We ascribe the lack of lesion phenotype to increased nocturnal ATP supply due to glycolytic degradation of starch which may lead to additional substrate-level phosphorylation in the stroma. Thus, nocturnal import of ATP into chloroplasts represents a crucial, previously unknown process that is required for controlled chlorophyll biosynthesis and for preventing photooxidative damage. [source] Cytochrome b6f mutation specifically affects thermal dissipation of absorbed light energy in ArabidopsisTHE PLANT JOURNAL, Issue 3 2001Yuri Munekage Summary Light-induced lumenal acidification controls the efficiency of light harvesting by inducing thermal dissipation of excess absorbed light energy in photosystem II. We isolated an Arabidopsis mutant, pgr1 (proton gradient regulation), entirely lacking thermal dissipation, which was observed as little non-photochemical quenching of chlorophyll fluorescence. Map-based cloning showed that pgr1 had a point mutation in petC encoding the Rieske subunit of the cytochrome b6f complex. Although the electron transport rate was not affected at low light intensity, it was significantly restricted at high light intensity in pgr1, indicating that the lumenal acidification was not sufficient to induce thermal dissipation. This view was supported by (i) slow de-epoxidation of violaXanthin, which is closely related to lumenal acidification, and (ii) reduced 9-aminoacridine fluorescence quenching. Although lumenal acidification was insufficient to induce thermal dissipation, growth rate was not affected under low light growth conditions in pgr1. These results suggest that thermal dissipation is precisely regulated by lumenal pH to maintain maximum photosynthetic activity. We showed that pgr1 was sensitive to changes in light conditions, demonstrating that maximum activity of the cytochrome b6f complex is indispensable for short-term acclimation. [source] | ||||||||||