Evidence that cytochrome b559 is involved in superoxide production in photosystem II: effect of synthetic short-chain plastoquinones in a cytochrome b559 tobacco mutant

摘要: Light-induced production of superoxide (O2*-) in spinach PSII (photosystem II) membrane particles was studied using EPR spin-trapping spectroscopy. The presence exogenous PQs (plastoquinones) with a different side-chain length (PQ-n, n isoprenoid units the side-chain) enhanced O2*- following order: PQ-1>PQ-2>>PQ-9. In isolated from tobacco cyt (cytochrome) b559 mutant which carries single-point mutation beta-subunit and also has decreased amount alpha-subunit, effect PQ-1 less than wild-type. increase LP (low-potential) content, induced by incubation at low pH, resulted significant formation PQ-1, whereas it had little on absence PQ-1. enhancement not abolished DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea]. Under anaerobic conditions, dark oxidation increased, as pH decreased. molecular oxygen significantly b559. Based these findings is suggested that short-chain stimulate via mechanism involves electron transfer Pheo- (pheophytin) to subsequent auto-oxidation