Effects of dark- and light-induced proton gradients in thylakoids on the Q and B thermoluminescence bands |
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Authors: | Teresa Miranda Jean Marc Ducruet |
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Affiliation: | (1) Section de Bioénergétique, DBCM, INRA/CEA Saclay, 91191 Gif-sur-Yvette Cedex, France |
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Abstract: | Thermoluminescence experiments have been carried out to study the effect of a transmembrane proton gradient on the recombination properties of the S2 and S3 states of the oxygen evolving complex with QA- and QB-, the reduced electron acceptors of Photosystem II. We first determined the properties of the S2QA- (Q band), S2QB- and S3QB- (B bands) recombinations in the pH range 5.5 to 9.0, using uncoupled thylakoids. The, a proton gradient was created in the dark, using the ATP-hydrolase function of ATPases, in coupled unfrozen thylakoids. A shift towards low temperature of both Q and B bands was observed to increase with the magnitude of the proton gradient measured by the fluorescence quenching of 9-aminoacridine. This downshift was larger for S3QB- than for S2QB- and it was suppressed by nigericin, but not by valinomycin. Similar results were obtained when a proton gradient was formed by photosystem I photochemistry. When Photosystem II electron transfer was induced by a flash sequence, the reduction of the plastoquinone pool also contributed to the downshift in the absence of an electron acceptor. In leaves submitted to a flash sequence above 0°C, a downshift was also observed, which was supressed by nigericin infiltration. Thus, thermoluminescence provides direct evidence on the enhancing effect of lumen acidification on the S3S2 and S2S1 reverse-transitions. Both reduction of the plastoquinone pool and lumen acidification induce a shift of the Q and B bands to lower temperature, with a predominance of lumen acidification in non-freezing, moderate light conditions.Abbreviations 9-AA 9-aminoacridine - EA activation energy - F0 constant fluorescence level - FM maximum fluorescence, when all PS-II centers are closed - FV variable fluorescence (FM–F0) - PS I, PS II Photosystem I, photosystem II - PQ plastoquinone - TL thermoluminescence |
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Keywords: | herbicide resistance Photosystem II proton gradient S states thermoluminescence |
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