Photoinhibition of electron transport activity of photosystem ii in isolated thylakoids studied by thermoluminescence and delayed luminescence

Abstract

The effect of photoinhibition on the primary (Qa) and secondary (Qb) quinone acceptors of photosystem II was investigated inisolated spinach thylakoids by the methods of thermoluminescence and delayed luminescence. The amplitudes of the Q (at about 2 °C) and B (at about 30 °C) thermoluminescence bands which are associated with the recombination of the S2QA− and S2QB charge pairs, respectively, exhibited parallel decay courses during photoinhibitorytreatment. Similarly, the amplitudes of the flash-induced delayed luminescence components ascribed to the recombination of S2QA− and S2QB− charge pairs and having half life-times of about 3 s and 30 s, respectively, declined in parallel with the amplitudes of the corresponding Q and B thermoluminescence bands. The course of inhibition of thermoluminescence and delayed luminescence intensity was parallel with that of the rate of oxygen evolution. The peak positions of the B and Q thermoluminescence bands as well as the half life-times of the corresponding delayed luminescence components were not affected by photoinhibition. These results indicate that in isolated thylakoids neither the amount nor the stability of the reduced OB acceptor is preferentially decreased by photoinhibition. We conclude that either the primary target of photodamage is located before the O b binding site in the reaction center of photosystem II or QA and QB undergo simultaneous damage. © 1988, Walter de Gruyter. All rights reserved.