MEASUREMENTS OF S(2)Q(B)(-) RECOMBINATION BY DELAYED THERMOLUMINESCENCE REVEAL HETEROGENEITY IN PHOTOSYSTEM-II ENERGETICS

The measurement of recombination kinetics from the S(2)Q(B)(-) state o f photosystem II (PS II) in spinach thylakoids using a thermoluminesce nce technique is described. Such measurements reveal that PS II exists in at least two substates with distinct kinetic and thermodynamic beh aviors. Since it is not affected by treatments to alter the formal red ox state of the PS II centers it was concluded that the heterogeneity is probably due to the existence of at least two conformational substa tes of the PS II proteins. The observed heterogeneity persists on a ti me scale or minutes at physiological temperatures, and thus is likely to be important for PS II function in vivo. (C) 1997 Elsevier Science Ltd. All rights reserved.