Formation of singlet oxygen and protection against its oxidative damage in Photosystem II under abiotic stress

Photosystem II (PSII) is exposed to various abiotic stresses associated with adverse environmental conditions such as high light, heat, heavy metals or mechanical injury. Distinctive functional response to adverse environmental conditions is formation of singlet oxygen (1O2). In this review, recent progress on mechanistic principles on 1O2 formation under abiotic stresses is summarized. Under high light, 1O2 is formed by excitation energy transfer from triplet chlorophylls to molecular oxygen formed by the spin conversion via photosensitization Type II reaction in the PSII antenna complex or by the recombination of 1[P680+Pheo−] radical pair in the PSII reaction center. Apart from well-described 1O2 formation by excitation energy transfer, 1O2 formation by decomposition of dioxetane and tetroxide is summarized as a potential source of 1O2 in PSII under heat, heavy metals and mechanical stress. The description of mechanistic principles on 1O2 formation under abiotic stress allows us to understand how plants respond to adverse environmental conditions in vivo.