Novel effects of methyl viologen on photosystem II function in spinach leaves |
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| Authors: | Da-Yong Fan Husen Jia James Barber Wah Soon Chow |
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| Affiliation: | (1) Photobioenergetics Group, School of Biology, College of Medicine, Biology and Environment, The Australian National University, Canberra, ACT, 0200, Australia;(2) State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, The Chinese Academy of Sciences, 100093 Beijing, China;(3) Division of Molecular Biosciences, Faculty of Science, Imperial College, London, SW7 2AZ, UK; |
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| Abstract: | Methyl viologen (MV) is a well-known electron mediator that works on the acceptor side of photosystem I. We investigated the little-known, MV-induced inhibition of linear electron flow through photosystem II (PS II) in spinach-leaf discs. Even a low [MV] decreased the (1) average, light-adapted photochemical efficiency of PS II traps, (2) oxidation state of the primary quinone acceptor QA in PS II during illumination, (3) photochemical efficiency of light-adapted open PS II traps, (4) fraction of absorbed light energy dissipated constitutively in a light-independent manner or as chlorophyll (Chl) a fluorescence emission, (5) Chl a fluorescence yield corresponding to dark-adapted open reaction-center traps (F o) and closed reaction-center traps (F m), and (6) half-time for re-oxidation of QA− in PS II after a single-turnover flash. These effects suggest that the presence of MV accelerates various “downhill” electron-transfer steps in PS II. Therefore, when using the MV to quantify cyclic electron flow, the inhibitory effect of MV on PS II should be taken into account. |
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