THE ACCEPTOR SIDE OF PHOTOSYSTEM II IN PHOTOSYNTHESIS *

Light absorbed by PS I l t of green Rlants leads to the oxidation of water to O2 and the reduction of the PQ pool. In this review, we shall restrict our discussion to the most important observations on the acceptor (quinone) side of PS 11, the part of the electron transport chain between the PS I 1 reaction center Chl a. P680, and the PQ pool (Fig. 1). This review will begin with a discussion of the primary electron acceptor of PS 11, pheophytin. followed by a discussion of the heterogeneity in the nexteelectron carrier, the quinone Qthe possible relationships between various suggested kinetic species of Q (Q1, Qz. Qz, Q,,, QL and QH) will be included; details of the back reaction of Q with P680’ will not be reviewed here (see e.g. Lavorel ~t a/. [98]. DeVault [41] and Govindjee and Jursinic [57]). We shall then present a review of a 32 kD protein associated with Q and with the next two-electron carrier the plastoquinone B; the actions of herbicides and of HCO; on electron transport in the Q/B region: action of some of the new electron transport inhibitors (diphenylamines. UHDBT. dinitrophenyl-