Transmembrane movements of artificial redox mediators in relation to electron transport and ionic currents in chloroplasts |
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Authors: | Alexander A. Bulychev Tijmen van Voorthuysen Wim J. Vredenberg |
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Affiliation: | Dept of Biophysics, Faculty of Biology, Moscow State Univ., Moscow 119899, Russia;Dept of Plant Physiology, Wageningen Agricultural Univ., Arboretumlaan 4, NL-6703 BD Wageningen, The Netherlands. |
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Abstract: | Electrochemical data obtained with TMPD+-sensitive electrodes indicate that ammonium-uncoupled chloroplasts retain TMPD (N,N,N',N'-tetramethyl- p -phenylenediamine) mainly in the reduced form during illumination, whereas uncoupled DCMU-treated chloroplasts accumulate TMPD in the oxidized form (TMPD+). This observation indicates that the reduced plastoquinol is the preferred electron donor for photosystem I (PSI) and TMPD can only compete efficiently when plastoquinone reduction is blocked. After adding DCMU the formation of a transmembrane gradient for TMPD+ is reflected by a slow-down of the electrogenic electron transport and by the emerging of the overshoot of the membrane current in the light-off response. A light-dependent increase in photoelectric current generated by chloroplasts in the presence of NH4Cl and TMPD is observed and considered to be caused by a reversible release of current limitation in the interfacial conductance barriers in the lumen. |
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Keywords: | Artificial cyclic electron transport ionic currents ion movement ion-selective electrodes patch-clamp technique pea Peperomia metallica Pisum sativum photocurrent |
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