Nostoc muscorum cells showed metal-induced decrease in the relative growth, pigment contents, O2 evolution, and Hill activity in response to lead (Pb2+) and cadmium (Cd2+) treatment, which was further accentuated with increase in metal exposure time and metal concentration. I50 concentrations (50% growth inhibitory concentrations) of Pb2+ and Cd2+ for growth of N. muscorum were 55 and 21 μg mL-1, respectively. These results indicated that the cells of N. muscorum were more susceptible to Cd2+ in comparison to Pb2+. The O2 production was relatively more sensitive to both heavy metals (I50: 16 and 10 μg mL-1 of Pb2+ and Cd2+, respectively) than the Hill activity (I50: 61 and 39 μg mL-1 of Pb2+ and Cd2+, respectively). Further, measurement of Hill activity in the presence of metals and electron donors showed that inhibition sites of both Pb2+ and Cd2+ were located on the oxidizing site of PSII. The chlorophyll a (Chl a) and phycobilisome (PB) fluorescence emission spectra showed that energy transfer from Chl a and PB to PSII reaction center was more susceptible to Cd2+ than Pb2+., S. Dixit, D. P. Singh., and Obsahuje bibliografii
To investigate the role of glycine betaine in photosynthesis under stress, a transgenic wheat (Triticum aestivum L.) line T6 overaccumulating glycine betaine and its wild type Shi4185 were used. Seedlings were exposed to conditions of drought (30%, PEG-6000), heat (40°C) and their combination. The results revealed ultrastructural damage to the chloroplast and thylakoid lamellae with the withered phenotype by both drought and heat stress, and the damage was exacerbated by the combination of drought and heat. The appearance of a K step in the typical O-J-I-P curve and the decrease of Hill activity indicated a reduction of oxygen evolving complex function caused by stress. The greater damage was found in wild type than T6. Overaccumulation of glycine betaine in T6 could protect lipids in the thylakoid membrane from damage and stabilize the index of unsaturated fatty acids under stress. A lower ratio of monogalactosyl diacylglycerol/digalactosyl diacylglycerol and higher phosphatidylglycerol content in the thylakoid membrane of T6 were also observed under stress. These effects can promote stability of the thylakoid membrane. Otherwise, glycine betaine overaccumulation decreased photoinhibition of PSII under stress. The results also suggest that xanthophyll cycle-dependent non-radiative energy dissipation may be involved in the GB-mediated effects on PSII function under stress conditions. and G. P. Wang ... [et al.].
The rate of accumulation of total chlorophyll (Chl) and carotenoids (Car) of leaves grown under high irradiance, HI (30 and 45 W m-2) was faster than at moderate irradiance, MI (15 W m-2). However, the senescence phase started earlier in the samples and proceeded at a faster rate. Chl a/b and Chl (a+b)/Car values showed faster loss of Chl a (compared to Chl b) and Chl (a+b) (compared to Car) in HI leaves. Protein accumulation and loss were also similar to that of Chl (a+b) content. Increase in Chl fluorescence during the development phase may suggest a gradual change in thylakoid organisation, however, the temporal kinetics were different in HI and MI samples. Increase in fluorescence polarisation during senescence of HI leaves compared to the control (MI) suggests conversion of thylakoid membranes to gel phase. Chloroplasts prepared from HI seedlings showed higher rate of photochemical activities, however, the activity declined earlier and at faster rate compared to the control. and Rajendra K. Behera, Nakul K. Choudhury.