Abstract: The role of D1 protein turnover，xanthophylls cycle and electron transport in protecting photosynthetic apparatus against photodamage in two-year old Satsuma mandarin（Citrus unishiu Marc.） detached leaves were investigated by using chlorophyll fluorescence，Western-blotting and inhibitors. The results showed that the initial fluorescence（Fo）increased significantly in leaves when exposed to high temperature and strong light（40 ℃，2 000 μmol • m-2 • s-1）for 30 min，on the other hand，maximum fluorescence（Fm），non-photochemical quenching（NPQ），maximal photochemical efficiency of PSⅡ（Fv/Fm）declined，and the D1 protein was degraded. Under high temperature and strong light，reduced levels of Fv/Fm，Fm，ETR（electron transport rate），ΦPSⅡ（quantum yield of PSⅡ）and content of D1 protein were observed in dithiothreitol（DTT，xanthophylls cycle inhibitor）or lincomycin（D1 synthesis inhibitor）-fed leaves compared to non-fed ones. More severe decrease occurred in lincomycin-treated leaves than that in DTT-treated ones. After DCMU（an inhibitor of electron transport）was added onto leaves，under high temperature and strong light，Fo level increased by 78%，Fv/Fm value，while D1 protein content decreased by 33% and 83% respectively. These results suggest that the xanthophylls cycle and the D1 protein turnover might play important role in protecting photosynthetic apparatus of Satsuma mandarin leaves against photodamage，and the contribution of the D1 protein turnover to photo-protect is prior to xanthophylls cycle. From our results，it is apparent that the D1 protein turnover might depend on electron transport.

Key words: citrus, Satsuma mandarin, high temperature and strong light, xanthophylls cycle, D1 protein, chlorophyll fluorescence