title: Novel effects of methyl viologen on photosystem II function in spinach leaves.
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 Q(A) 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 Q (A) (-) 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.
authors.affiliation: Photobioenergetics Group, School of Biology, College of Medicine, Biology and Environment, The Australian National University, Canberra, ACT, 0200, Australia.
authors.forename: Da-Yong
authors.initials: DY
authors.lastname: Fan
authors.forename: Husen
authors.initials: H
authors.lastname: Jia
authors.forename: James
authors.initials: J
authors.lastname: Barber
authors.forename: Wah Soon
authors.initials: WS
authors.lastname: Chow
mesh_terms: D000042:Absorption; D000222:Adaptation, Physiological / Q000187:drug effects; D002734:Chlorophyll / Q000378:metabolism; D003624:Darkness; D004579:Electron Transport / Q000187:drug effects; D007700:Kinetics; D010269:Paraquat / Q000494:pharmacology*; D055668:Photochemical Processes / Q000187:drug effects; D045331:Photosystem I Protein Complex / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000187:drug effects* / Q000201:enzymology*; D013050:Spectrometry, Fluorescence; D018724:Spinacia oleracea / Q000187:drug effects* / Q000201:enzymology*
chemical_list: D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D010269:Paraquat