Measurement of degree of chlorophyll fluorescence polarization in relation to the regulation of excitation energy transfer between Photosystems I and II in pea chloroplasts |
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Authors: | Y. Yamamoto J. Barber |
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Affiliation: | ARC Photosynthesis Research Group, Department of Pure and Applied Biology, Imperial College, London S.W.7.2BB U.K. |
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Abstract: | The degree of chlorophyll fluorescence polarization (p) at 740 nm was measured at room temperature for pea chloroplasts subjected to various conditions. (1) In agreement with previous published observations, p decreased when the Photosystem (PS) II traps were closed by illumination in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. (2) Under these conditions, the magnitude of p was also sensitive to the presence of salts. Under conditions when ‘spillover’ of the excitation energy from PS II to PS I was low, p was also low, being consistent with increased migration of energy between the PS II light-harvesting chlorophylls. In contrast, when spillover was at a maximum p increased. (3) The change in p in the presence of salts was dependent on the concentration and valency of the cations in such a way as to suggest the changes were mediated through electrostatic forces. The dependency of p on ionic composition of the experimental medium was closely related to the associated changes in fluorescence yield. (4) Membrane stacking, caused by lowering pH of the chloroplast suspension, did not induce a significant change in p, suggesting that this pH-induced process is different from the membrane stacking brought about by manipulating the salt levels. (5) Incubation of thylakoids with ATP induces light-dependent phosphorylation of the light-harvesting chlorophyll-protein complexes, and regulates excitation energy transfer between PS I and PS II (Bennett, J., Steinback, K.R. and Arntzen, C.J. (1980) Proc. Natl. Acad. Sci. U.S.A. 77, 5253–5257). Under conditions which bring about this phosphorylation it was found that p increased to a value indicative of spillover. |
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Keywords: | Chlorophyll fluorescence Fluorescence polarization Excitation energy transfer Cation effect Photosynthesis (Pea chloroplast) PS photosystem Chl chlorophyll DCMU 3-(3,4-dichlorophenyl)-1, 1-dimethylurea Hepes Mes |
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