PARTICIPATION OF THE G = 1.9 AND G = 1.82 EPR FORMS OF THE SEMIQUINONE-IRON COMPLEX Q(A)(-).FE2+ OF PHOTOSYSTEM-II IN THE GENERATION OF THE Q AND C THERMOLUMINESCENCE BANDS, RESPECTIVELY

Following illumination at 200 K, the charge recombination reactions and the origin of the thermoluminescence (TL) bands appearing at about O-degrees-C (Q band) and +50-degrees-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-degrees-C and +25-degrees-C, respectively, suggest that the S2 state (multi-line signal) undergoes charge recombination with the g = 1.9 form of the semiquinone-iron complex, Q(A)- . Fe2+, resulting in the appearance of the Q band, and that the g = 1.82 form of Q(A)- . Fe2+ back-reacts with the oxidized tyrosine, Y(D)+ (Signal II(s)), accounting for the generation of the C band.