Interaction of N,N,N′,N′-tetramethyl- p-phenylenediamine with photosystem II as revealed by thermoluminescence: Reduction of the higher oxidation states of the Mn cluster and displacement of plastoquinone from the Q B niche

Abstract

The flash-induced thermoluminescence (TL) technique was used to investigate the action of N,N,N′,N′-tetramethyl- p-phenylenediamine (TMPD) on charge recombination in photosystem II (PSII). Addition of low concentrations (μM range) of TMPD to thylakoid samples strongly decreased the yield of TL emanating from S 2Q B − and S 3Q B − (B-band), S 2Q A − (Q-band), and Y D +Q A − (C-band) charge pairs. Further, the temperature-dependent decline in the amplitude of chlorophyll fluorescence after a flash of white light was strongly retarded by TMPD when measured in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Though the period-four oscillation of the B-band emission was conserved in samples treated with TMPD, the flash-dependent yields (Y n) were strongly declined. This coincided with an upshift in the maximum yield of the B-band in the period-four oscillation to the next flash. The above characteristics were similar to the action of the ADRY agent, carbonylcyanide m-chlorophenylhydrazone (CCCP). Simulation of the B-band oscillation pattern using the integrated Joliot–Kok model of the S-state transitions and binary oscillations of Q B confirmed that TMPD decreased the initial population of PSII centers with an oxidized plastoquinone molecule in the Q B niche. It was deduced that the action of TMPD was similar to CCCP, TMPD being able to compete with plastoquinone for binding at the Q B-site and to reduce the higher S-states of the Mn cluster.