PHOTOINHIBITION OF PHOTOSYNTHESIS IN-VIVO - THE ROLE OF PROTEIN-TURNOVER IN PHOTOSYSTEM-II

Divergent theories on the mechanism behind, and the nature of, photoin hibition are discussed, especially in relation to observations made in higher plant leaves. Comparisons are made with 'lower' plane groups a nd results of in vivo and in vitro experiments are considered. Irradia nce-induced mechanisms involved in the regulation of PSII function and structure are discussed in connection with turnover of the D1 protein . A model is presented in which a structural change in D1 protein faci litates the formation of a population of dissipative PSII centres that do not participate in linear electron transport to PSI. We suggest a sophisticated regulatory mechanism whereby this variable PSII function is controlled with respect to both incident light and biochemical dem and, a control which relies on feedback from both light and dark react ions.