Photosynthetic electron transport activity in heat-treated barley leaves: The role of internal alternative electron donors to photosystem II |
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| Authors: | Szilvia Z. Tó th,Gert Schansker,Reto J. Strasser |
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| Affiliation: | a Laboratory of Bioenergetics, University of Geneva, Chemin des Embrouchis 10, CH-1254 Jussy, Geneva, Switzerland
b Institute of Plant Biology, Biological Research Center of the Hungarian Academy of Sciences, PO Box 521, H-6701 Szeged, Hungary |
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| Abstract: | Electron transport processes were investigated in barley leaves in which the oxygen-evolution was fully inhibited by a heat pulse (48 °C, 40 s). Under these circumstances, the K peak (∼ F400 μs) appears in the chl a fluorescence (OJIP) transient reflecting partial QA reduction, which is due to a stable charge separation resulting from the donation of one electron by tyrozine Z. Following the K peak additional fluorescence increase (indicating QA− accumulation) occurs in the 0.2-2 s time range. Using simultaneous chl a fluorescence and 820 nm transmission measurements it is demonstrated that this QA− accumulation is due to naturally occurring alternative electron sources that donate electrons to the donor side of photosystem II. Chl a fluorescence data obtained with 5-ms light pulses (double flashes spaced 2.3-500 ms apart, and trains of several hundred flashes spaced by 100 or 200 ms) show that the electron donation occurs from a large pool with t1/2 ∼ 30 ms. This alternative electron donor is most probably ascorbate. |
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| Keywords: | Asc, ascorbate DCMU, 3-(3&prime ,4&prime -dichlorophenyl)-1,1-dimethylurea Fd, ferredoxin F0, initial fluorescence (measured at 20 μs), all PSII RCs are open FJ, fluorescence intensity at &sim 3 ms (at 3000 μmol photons m&minus 2 s&minus 1) FM, maximum fluorescence, all PSII RCs are closed FNR, ferredoxin-NADP+-reductase FP, maximum measured fluorescence intensity FR, far-red light I820nm, transmission at 820 nm I, step in the OJIP transient at 30 ms J, step in the OJIP transient at &sim 3 ms (at 3000 μmol photons m&minus 2 s&minus 1) K, peak in the OJIP transient at &sim 400 μs (at 3000 μmol photons m&minus 2 s&minus 1) MV, methylviologen, 1,1&prime -dimethyl-4,4&prime -bipyridinium-dichloride OEC, oxygen evolving complex OJIP, chl a fluorescence transient defined by the names of its intermediate steps PpBQ, phenyl-p-benzoquinone P680, primary electron donor of PSII P700, primary electron donor of PSI PC, plastocyanin PQ, plastoquinone PSI, photosystem I PSII, photosystem II QA, primary electron acceptor quinone of PSII QB, secondary electron acceptor quinone of PSII TyrZ, tyrozine Z φPo, maximum quantum yield for primary photochemistry |
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