Identification and characterization of Arabidopsis mutants with reduced quenching of chlorophyll fluorescence.

Regulation of nonradiative dissipation of absorbed light energy in PSII is an indispensable process to avoid photoinhibition in plants. To dissect molecular mechanisms of the regulation, we identified Arabidopsis mutants with reduced quenching of Chl fluorescence using a fluorescence imaging system. By analyses of Chl fluorescence induction pattern in the light and quantum yield of both photosystems, 37 mutants were classified into three groups. The first group was characterized by an extremely high level of minimum Chl fluorescence at the open PSII center possibly due to a defect in PSII. Mutants with significant reduction in the nonphotochemical quenching formation but not in quantum yield of both photosystems were classified into the second group. Mutants in the third group showed reduction in quantum yield of both photosystems possibly due to a defect in the electron transport activity. Mutants in the second and third groups were further characterized by light intensity dependence of Chl fluorescence parameters and steady state redox level of P700.