Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10841071 | Plant Science | 2005 | 6 Pages |
Abstract
The effects of high temperature (30-52.5 °C) on electron transport at the acceptor side of photosystem II (PSII) in a cyanobacterium Spirulina platensis grown at 30 °C were studied by measuring the relaxation of flash-induced variable chlorophyll fluorescence. In order to investigate the reversibility of the effects of heat stress on electron transport at the acceptor side of PSII, heat-induced effects were measured either immediately after the cells were treated at high temperature for 5 min or after the heat-treated cells were cooled down to the growth temperature and incubated for another 5 min. The maximal efficiency of PSII photochemistry (Fv/Fm) decreased significantly with increasing temperature when measured immediately after the temperature treatment. Fv/Fm showed only a partial recovery (5-15%) when the heat-treated cells were cooled down to the growth temperature and incubated for another 5 min. The decrease in Fv/Fm was a result of a considerable increase in the minimal fluorescence yield and a significant decrease in the maximal fluorescence yield. Heat stress affected considerably the relaxation of flash-induced variable chlorophyll fluorescence. The amplitudes of the fast (â160 μs) and the middle (â2 s) components, assigned to electron transfer from QAâ to QB site and the diffusion of PQ molecules to an empty QB site, respectively, decreased significantly with increasing temperature. On the other hand, the slow component (â4 s) due to the charge recombination from the S2QAâ state of the water oxidation to the S1QA state, increased significantly. These results suggest that heat stress leads to the inhibition of electron transport from QAâ to QB, the binding affinity of a PQ molecule to the QB-binding site, and the increased probability of back electron transfer from QAâ to S2 state at the expense of forward electron flow. However, these changes in the function of the acceptor side of PSII were mostly recovered after 5 min incubation at the growth temperature.
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Authors
Xiaogang Wen, Hongmei Gong, Congming Lu,