The light-intensity-dependence of the efficacy of 2-(3-chloro-4-trifluoromethyl)-anilino-3,5-dinitrothiophene (Ant2p) to inhibit the photosystem 2 reactions of chloroplasts

Abstract

The mechanism by which Ant2p [2-(3-chloro-4-trifluoromethyl)anilino-3,5-dinitrothiophene] inhibits the O2 evolution capacity of chloroplasts [of Pisum sativum] is thought to be due to a rapid reduction of the S2 and S3 oxidation states of the O2-evolving complex mediated by the oxidation of endogenous donors such as cytochrome b559. The degree of inhibition by Ant2p of the photosystem 2-supported electron transfer reactions, registered by the light-dependent rate of dichlorophenolindophenol reduction, varies according to the actinic light intensity. A similar intensity-dependence can be detected in the extent of the Ant2p-induced cytochrome b559 HP photo-oxidation. The dependence of the cytochrome oxidation is not due to the oxidation per se, but reflects changes in the high light-driven re-reduction reaction. The close correlation between the 2 Ant2p reactions is interpreted as indicating that the effect of Ant2p might be due to an inhibition of the S-state turnovers and not necessarily due to a deactivation process.