The effects of ultraviolet irradiation on P680+ reduction in PS II core complexes measured for individual S-states and during repetitive cycling of the oxygen-evolving complex |
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Authors: | Adele Post P. B. Lukins P. J. Walker A. W. D. Larkum |
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Affiliation: | (1) School of Biological Sciences, A12, University of Sydney, 2006, N.S.W., Australia;(2) School of Physics, A28, University of Sydney, 2006, N.S.W., Australia |
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Abstract: | Flash-induced absorbance measurements at 830 nm on both nanosecond and microsecond timescales have been used to characterise the effect of ultraviolet light on Photosystem II core particles. A combination of UV-A and UV-B, closely simulating the spectrum of sunlight below 350 nm, was found to have a primary effect on the donor side of P680. Repetitive measurements indicated reductions in the nanosecond components of the absorbance decay with a concomitant appearance and increase in the amplitude of a component with a 10 s time constant attributed to slow reduction of P680+ by Tyrz when the function of the oxygen evolving complex is inhibited. Single-flash measurements show that the nanosecond components have amplitudes which vary with S-state. Increasing UV irradiation inhibited the amplitude of these components without changing their S-state dependence. In addition, UV irradiation resulted in a reduction in the total amplitude, with no change in the proportion of the 10 s contribution.Abbreviations BBY- PS II membrane fragments - P680- primary electron donor of PS II - PS II- Photosystem II - QA and QB– primary and secondary quinone electron acceptors of PS II - S-state- redox state of the oxygenevolving complex - Tyrz– tyrosine residue in PS II - UV-A- ultraviolet radiation 320–400 nm - UV-B- ultraviolet radiation 280–320 nm |
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Keywords: | Photosystem II core complex P680+ reduction kinetics S-state ultraviolet radiation |
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