Effects of short-term exposure to different irradiances on the function of photosystem 2 (PS2) were studied for barley grown at low (LI; 50 µmol m-2 s-1) and high (HI; 1 100 µmol m-2 s-1) irradiances. HI barley revealed higher ability to down-regulate the light-harvesting within PS2 after exposure to high irradiance as compared to LI plants. This ability was estimated from the light-induced decreases of F685/F742 and E476/E436 in emission and excitation spectra of 77 K chlorophyll (Chl) a fluorescence in vivo which was 65 and 10 % for HI plants as compared to 30 and 2 % for LI plants, respectively. For LI plants this protective down-regulation of the light-harvesting of PS2 was saturated at 430 µmol m-2 s-1, and progressive PS2 photodamage was induced at higher irradiances. After exposure of LI segments to 2 200 µmol m-2 s-1 a pronounced maximum at 700 nm appeared in emission spectrum of 77 K Chl a fluorescence. Based on complementary analysis of 77 K excitation spectra measured at the emission wavelength 685 nm we suggest that this emission maximum may be attributed to the formation of aggregates of light-harvesting complexes of PS2 (LHC2) with part of PS2 core during progressive PS2 photodamage. Our results can be explained assuming different contributions of LHC2 and PS2 core to the total nonradiative dissipation of absorbed excitation energy for the LI and HI barley. and M. Čajánek ... [et al.].
a1_To determine how the use of a given rootstock can influence the functioning of the photosynthetic apparatus of the scion under salt stress, the growth, gas exchange, photosystem II (PSII) efficiency, xanthophyll cycle, and chloroplast ultrastructure of nongrafted,
self-grafted, and pumpkin-grafted (hereafter referred to as rootstock-grafted) cucumber (Cucumis sativus L.) plants were investigated at day 15 after being treated with 90 mM NaCl. The reductions in plant growth of the rootstock-grafted plants were lower than those of the nongrafted and self-grafted plants under 90 mM NaCl. The net photosynthetic rate, stomatal conductance, maximal and effective quantum yield of PSII photochemistry, photochemical quenching coefficient, and effective quantum-use efficiency of PSII in the light-adapted state of the nongrafted and self-grafted plants were significantly decreased under 90 mM NaCl. However, these reductions were alleviated when the cucumber plants were grafted onto the pumpkin (Cucurbita moschata Duch.) rootstock. The intercellular CO2 concentrations were significantly increased in the nongrafted and self-grafted plants under 90 mM NaCl, whereas it was decreased in the rootstock-grafted plants. Nonphotochemical quenching (NPQ) and the deepoxidation state of the xanthophyll cycle were significantly increased under 90 mM NaCl, particularly in the rootstockgrafted plants, suggesting the rootstock-grafted plants had higher potential to dissipate excess excitation energy and reduce the probability of photodamage to PSII. Under 90 mM NaCl, the number of grana was reduced, the thylakoids were swollen, and starch granules accumulated in all plants. However, the damage of chloroplast ultrastructure was alleviated in the rootstock-grafted plants., a2_Taken together, the use of C. moschata rootstock alleviated salt stress in cucumber plants by delaying photoinhibition, probably due to a lower incidence of both stomatal and nonstomatal factors limiting photosynthesis., Z. X. Liu ... [et al.]., and Obsahuje bibliografii
Two pearl millet [Pennisetum glaucum (L.) R. Br. emend. Stuntz] hybrids GHB-30 and MH-179 were given defoliation treatments prior to anthesis comprising zero leaf to intact control. Keeping or removing even flag leaf only significantly altered the grain yield. With increasing leaf area (leaf numbers) the grain yield also significantly increased. Test mass showed more or less a similar trend. The leaves in the upper portion (nearer to sink) showed a greater contribution to the grain yield than the lower ones (away from sink). However, the highest leaf efficiency in terms of contribution per unit leaf area and the contribution by the whole leaf to the grain yield was recorded by 4th and 3rd leaf, respectively. The stem (covered with petioles) contributed to the extent of around 12 %. The existing leaves compensated to some extent for the defoliated ones. and A. K. Joshi ... [et al.].
Arabidopsis thaliana L., ch1-1 (chlorophyll b-less mutant), gi-1 (GI deficient mutant), cry2-1 (blue-light-photoreceptor CRY2 deficient mutant), and Columbia (Col; wild ecotype) were grown under broad range of irradiances (I) from the beginning of germination and the effect of I on the survival, development, and flowering was studied. Under low and moderate I (<300 µmol m-2 s-1), flowering time and plant size at flowering showed great variations among ch1-1, gi-1, cry2-1, and Col, whereas under higher I (>500 µmol m-2 s-1), these characteristics were almost the same. Hence under high I, development and flowering of ch1-1, gi-1, cry2-1, and Col converged to almost the same state. Flowering time was negatively correlated with I, and under high I acclimation in A. thaliana was associated with a decrease in chlorophyll (Chl) content and increases in xanthophyll cycle pool and membrane-bound APX activity (EC 1.11.1.11) suggesting that an increase in oxidative stress induces earlier flowering. The plants of gi-1 and cry2-1 survived but Col and ch1-1 died under 1 000 µmol m-2 s-1, showing that mutants deficient in GI or CRY2 are more photo-stress-tolerant than Col and the Chl b-less mutant. Hence high I promotes in plants of Arabidopsis raised from germination till flowering the development and flowering time involving modulation of the photosynthetic apparatus, and this promoting effect is independent of the functions of flower-inducing GI or CRY2 gene. This can be regarded as photo-acclimation of A. thaliana for survival and reproduction under high I. and S. Moharekar ... [et al.].
Adding green component to growth light had a profound effect on biomass accumulation in lettuce. However, conflicting views on photosynthetic efficiency of green light, which have been reported, might occur due to nonuniform light sources used in previous studies. In an attempt to reveal plausible mechanisms underlying the differential photosynthetic and developmental responses to green light, we established a new way of light treatment modeled according to the principle of gene "knock out". Lettuce (Lactuca sativa L. var. youmaicai) was grown under two different light spectra, including a wide spectrum of light-emitting diode (LED) light (CK) and a wide spectrum LED light lacking green (480-560 nm) (LG). Total PPFD was approximately 100 µmol(photon) m-2 s-1 for each light source. As compared to lettuce grown under CK, shoot dry mass, photosynthetic pigment contents, total chlorophyll to carotenoids ratio, absorptance of PPFD, and CO2 assimilation showed a remarkable decrease under LG, although specific leaf area did not show significant difference. Furthermore, plants grown under LG showed significantly lower stomatal conductance, intercellular CO2 concentration, and transpiration compared with CK. The plants under CK exhibited significantly higher intrinsic quantum efficiency, respiration rate, saturation irradiance, and obviously lower compensation irradiance. Finally, we showed that the maximum ribulose-1,5-bisphosphate-saturated rate of carboxylation, the maximum rate of electron transport, and rate of triosephosphate utilization were significantly reduced by LG. These results highlighted the influence of green light on photosynthetic responses under the conditions used in this study. Adding green component (480-560 nm) to growth light affected biomass accumulation of lettuce in controllable environments, such as plant factory and Bioregenerative Life Support System., H. Liu, Y. Fu, M. Wang, H. Liu., and Obsahuje bibliografii