Analysis of photosystem II triplet states in thylakoids by fluorescence detected magnetic resonance in relation to the redox state of the primary quinone acceptor Q(A).

The dependence of PSII triplet populations as a function of the primary quinone acceptor QA redox state has been investigated by means of the fluorescence detected magnetic resonance (FDMR) technique in isolated thylakoid membranes. The results show that the population level of a microsecond decaying component having zero field splitting parameters |D|=0.0292 cm-1 and |E|=0.0037 cm-1 is inversely correlated to that of the recombination triplet (|D|=0.0285 cm-1 |E|=0.045 cm-1). The results could be interpreted in terms of the fast (50–150 s) decaying population being either the recombination triplet when the primary quinone QA is singly reduced or a triplet located on a chlorophyll which is in tight singlet transfer coupling with the primary donor.