The effect of magnesium and phosphorylation of light-harvesting chlorophyll ab-protein on the yield of P-700-photooxidation in pea chloroplasts |
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Authors: | Alison Telfer Hervé Bottin James Barber Paul Mathis |
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Institution: | 1. ARC Photosynthesis Research Group, Department of Pure and Applied Biology, Imperial College, London, SW7 2BB U.K.;2. Service de Biophysique, Département de Biologie, Centre d''Etudes Nucléaires de Saclay, 91191 Gif-sur-Yvette France |
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Abstract: | The yield of P-700 photooxidation has been studied in isolated chloroplast membranes by measuring the extent of the flash-induced absorption increase at 820 nm (ΔA820) in the microsecond time range. The extent of ΔA820 induced by non-saturating laser flashes was increased by the following treatments. (1) Suspension of chloroplast membranes in Mg2+ free medium (plus 15 mM K+) which leads to unstacking of grana (as detected by a decrease in chlorophyll fluorescence). (2) Reduction of Q, the primary acceptor of Photosystem II, in the presence of 20 μM 3-(3,4 dichlorophenyl)-1,1-dimethylurea by a saturating xenon flash, fired 300 ms before the laser flash. (3) Phosphorylation of light harvesting chlorophyll complex, which occurs in the presence of ATP after activation of protein kinase in the dark with NADPH and ferredoxin. We conclude that the Mg2+ concentration, the redox state of Q and the protein-phosphorylation all can control the photochemical efficiency of P-700 photooxidation in isolated chloroplasts, and we discuss these results in relation to control of excitation energy distribution between the two photosystems. We also discuss the significance of these results in relation to the regulation of photosynthetic electron transport in vivo. |
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Keywords: | Photosynthesis Protein phosphorylation Light-harvesting complex P-700 photooxidation Fluorescence Chl chlorophyll DCMU 3-(3′ 4′ dichlorophenyl)-1 1-dimethylurea DPIP 2 6-dichlorophenolindophenol maximum chlorophyll fluorescence yield initial chlorophyll fluorescence yield LHCP PS Photosystem Q primary acceptor of Photosystem II Tricine |
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