Rapid turnover of the RCII-D1 protein in the dark induced by photoinactivation of Photosystem II in Scenedesmus wild type and the PS-II-donor defective LF-1 mutant cells

AbstractWe have investigated the photoinactivation and turnover of the photochemical reaction centre II (RCII) D1 protein in Scenedesmus obliquus wt and LF-1 mutant containing an unprocessed precursor D1 protein (pD1) and defective in donor side activity of Photosystem II (PS II). Photoinactivation of PS II is considerably faster in the LF-1 mutant as compared to the wt cells. The RCII-D1(pD1) protein in photoinactivated cells is irreversibly modified and can be degraded and synthesised in the dark (turnover). Turnover of the D1 protein is proportional to the initial degree of photoinactivation. Diuron retards significantly the protein degradation in the photoinactivated cells. Wild-type cells photoinactivated in the presence of diuron exhibit a fluorescence induction transient similar to that of the LF-1 mutant. Removal of diuron allows rapid turnover of photoinactivated RCII-D1(pD1) in the dark. The protective effect of diuron is gradually lost in photoinactivated cells even when incubated in the dark. Blocking chloroplast translation activity does not prevent D1(pD1) protein degradation. We conclude that the irreversible changes induced by photoinactivation of RCII-D1(pD1) protein in vivo are sufficient to allow complete D1 protein turnover in the dark. Redox control of the D1 protein degradation in vivo is thus related to availability of oxidised plastoquinone which affects the access of the modified protein to the cleavage system (Gong and Ohad (1991) J. Biol. Chem. 266, 21293–21299.