THE IRREVERSIBLE PHOTOINHIBITION OF THE PHOTOSYSTEM-II COMPLEX IN LEAVES OF VICIA-FABA UNDER STRONG LIGHT

Exposure of the photosynthetic machinery to strong light causes the ph otoinhibition of the photosystem II complex. The recovery from the pho toinhibition ill vivo was characterized by monitoring the ratio of var iable to maximum fluorescence (F-v/F-m) in detached leaves of broad be an (Vicia faba). The changes in the ratio were explained in terms of t hree components, namely, two saturating exponential components with ha lf rise-times of about 15 and 120 min, respectively, and a non-recover y component. The non-recovery component increased gradually as the exp osure to strong light was prolonged. Our results suggest that this irr eversible component of the photoinhibition of the photosystem II compl ex was caused by severe stress due to strong light under which repair of the photosystem II complex was insufficient to allow full recovery. The irreversible photoinhibition is discussed in terms of both the ph ysiology and ecology of plants. (C) 1997 Elsevier Science S.A.