Abstract:

In order to study the effect of strong light on photosynthetic characteristics of Ginkgo biloba leaves, the photoinhibition and photoprotection mechanisms were investigated by analyzing chlorophyll a fluorescence parameters and pigment composition of the xanthophyll cycle when G.biloba leaves were exposed to strong light (1 200μmol photons·m^-2s^-1). During 5 h strong light stress, maximal photochemical efficiency of PSⅡ (F_vF_m) inG.biloba leaves decreased markedly, with the value of 0.3 forF_vF_m at the end of stress. On the contrary, initial fluorescence yield (F_o) increased obviously during the whole stress. Both non cyclic electron transport efficiency (Ф_PSⅡ) and apparent electron transport rate (ETR) decreased markedly under strong light (1 200μmol photons·m^-2s^-1). Hot dissipation of antenna (HDR) increased during the stress. The increase of non-photochemical quenching (NPQ) was accompanied by the increase of relative contents of zeaxanthin (Z) during the time course of stress. The results showed that severe photoinhibition occurred in G.biloba leaves, HDR and the xanthophyll cycle dependent NPQ were valid to alleviate strong light damage by dissipating excess energy efficiently in G.biloba leaves. However, reversible inactivation of PSⅡ centers was the main factor causing the decrease of F_vF_m.

Key words: Gingko biloba, Photoinhibition, Xanthophyll cycle, Strong light stress, Photoprotection mechanism