Abstract:Leaf discs of spinach were exposed to high light in the presence of active oxygen,protein modifiers and denaturants, and chlorophyll fluorescence kinetics was detected and compared with high light treatment alone.The addition of H2O2, O2-, OH and 'O2 enhanced photoinhibition, showing the decrease of Fv/Fm, qp and PSⅡ, which were accompanied by the increase of qN and 1 -qp. Treatment of four protein modifiers, NBS, DEPC, BDE and pCMB, also exhibited the similar changes of fluorescence parameters. More evident change was caused by BDE, an Arg-modifier of protein. SDS affected significantly on Fm, Fv and qp, but didn't change qN. A complete lose of qp associated with maximum qN were induced by Gu-HCl. Urea and DMSO at low concentration reduced the PSⅡ activitv and increased qN in less extent. The results suggest that any change in conformation or structure of chloroplast protein all led to the enhancement of PSll photoinactivation.