Photoinhibition of oxygen-evolving complex and photosystem II at chilling stress in the tropical tree species Dalbergia odorifera

Photosystem II is sensitive to chilling stress in tropical tree species. However, the underlying mechanism is not clear. In this study, we examined the effects of chilling and light stress on activities of PSII and oxygen-evolving complex (OEC), in order to resolve the controversy of whether chilling-induced PSII photoinhibition is attributed to the excess-energy model or the two-step scheme. We determined changes in chlorophyll a fluorescence transient and energy distribution in PSII during treatment at chilling-light stress for the tropical tree species Dalbergia odorifera. At chilling temperature, the light-use efficiency was largely inhibited. During chilling treatment, the maximum quantum yield of PSII gradually decreased. Meanwhile, the relative fluorescence intensity at K-step (300 mu s) significantly increased, indicating the photodamage to OEC. A tightly positive correlation was found between photodamage to OEC and PSII photoinhibition, suggesting that photodamage to OEC was a rate-limiting step for PSII photoinhibition. Furthermore, additional generation of reactive oxygen species did not aggravate PSII photoinhibition at chilling temperature. These results suggest that two-step model is responsible for chilling-induced PSII photoinhibition in the tropical tree species D. odorifera.