Singlet oxygen formation detected by near-infrared emission from isolated photosystem II reaction centres: direct correlation between P680 triplet decay and luminescence rise kinetics and its consequences for photoinhibition

The kinetics of the quenching of the triplet state of P680 and the formation of singlet oxygen (O-1(2)) have been measured under various conditions using isolated photosystem II reaction centres (PSII RCs). The results support the hypothesis that light-induced generation of O-1(2) by PSII RCs is due to the formation of the P680 triplet state by the recombination reaction between oxidized P680 and reduced pheophytin. This suggests that singlet oxygen is likely to bring about protein damage, particularly to the D1 polypeptide, and that this detrimental reaction thus underlies the vulnerability of PSII to photoinhibitory damage. (C) 1999 Elsevier Science S.A. All rights reserved.