Mechanism of photoinhibition: photochemical reaction center inactivation in system II of chloroplasts |
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Authors: | Robyn E Cleland Anastasios Melis Patrick J Neale |
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Institution: | (1) Division of Molecular Plant Biology, University of California, 313 Hilgard Hall, 94720 Berkley, CA, USA;(2) Present address: Botany Department, Australian National University, GPO Box 4, 2601 Canberra City, ACT, Australia;(3) Department of Molecular Plant Biology, University of California, 313 Hilgard Hall, 94720 Berkeley, CA, USA |
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Abstract: | Photoinhibition of photosynthesis is manifested at the level of the leaf as a loss of CO2 fixation and at the level of the chloroplast thylakoid membrane as a loss of photosystem II electron-transport capacity. At the photosystem II level, photoinhibition is manifested by a lowered chlorophyll a variable fluorescence yield, by a lowered amplitude of the light-induced absorbance change at 320 nm ( A320) and 540-minus-550 nm ( A540–550), attributed to inhibition of the photoreduction of the primary plastoquinone QA molecule. A correlation of the kinetics of variable fluorescence yield loss with the inhibition of QA photoreduction suggested that photoinhibited reaction centers are incapable of generating a stable charge separation but are highly efficient in the trapping and non-photochemical dissipation of absorbed light. The direct effect of photoinhibition on primary photochemical parameters of photosystem II suggested a permanent reaction center modification the nature of which remains to be determined.Dedicated to Prof. L.N.M. Duysens on the occasion of his retirement |
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Keywords: | photosystem II charge separation fluorescence photoinhibition |
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