Effect of pH on the slow phase components of delayed luminescence in chloroplasts

Abstract

The pH dependence of two, flash-induced slowly decaying delayed luminescence com ponents—resulting from charge recombination of QA-; and QB-with the S2andS3states(S2QA-+ S3QA-and S2QB-+ S3, QB3irecombinations)—in untreated and herbicide treated chloroplasts was investigated within a pH range of 5.5 to 8.5. The component associated with QA-;showed the same pH-dependence in untreated and inDCMU-treated chloroplasts:its half-decay time increased wth increasing pH reflecting an appr.+5m eV/pH change in the free energy of activation. Contrary to this the component associated with Qb exhibited an opposite behaviour: its half-decay time d ecreased with increasing pH and the free energy of activation changed with about—5 m eV /pH. It is concluded that both acceptor and donor side effects are involved in the pH-dependence of slow phase delayed luminescence components. © 1987, Walter de Gruyter. All rights reserved.