Participation of the g = 1.9 and g = 1.82 EPR forms of the semiquinone-iron complex, Q A−·Fe 2+ of photosystem II in the generation of the Q and C thermoluminescence bands, respectively

Abstract

Following illumination at 200 K, the charge recombination reactions and the origin of the thermoluminescence (TL) bands appearing at about 0°C (Q band) and +50°C (C band) in the glow curve were investigated by comparative TL and EPR measurements in DCMU-treated photosystem II particles. Decay half-time measurements carried out at −25°C and +25°C, respectively, suggest that the S 2 state (multi-line signal) undergoes charge recombination with the g = 1.9 form of the semiquinone-iron complex, Q A −·Fe 2+, resulting in the appearance of the Q band, and that the g = 1.82 form of Q A −·Fe 2+ back-reacts with the oxidized tyrosine, Y D + (Signal II s), accounting for the generation of the C band.