Light-induced increase in initial chlorophyll fluorescence F-o level and the reversible inactivation of PSII reaction centers in soybean leaves

With a portable PAM-2000 fluorometer it was observed that responses of init ial chlorophyll fluorescence F-o level to strong light were different in va rious plant species examined. When the photochemical efficiency of Photosys tem II, F-v/F-m, declined, F-o increased significantly in leaves of some pl ants such as soybean and cotton, while F-o decreased remarkably in other pl ants such as wheat and barley. In order to explore the mechanism of the inc rease in F-o in soybean leaves, the change in D1 protein amount and effects of lincomycin and far-red light on these fluorescence parameters were obse rved by SDS-PAGE combined with gel scanning and chlorophyll fluorescence an alysis. The following results were obtained. (1) The amount of inactive PS II reaction centers increased under strong light and decreased during subse quent dark recovery [Hong and Xu (1997) Chinese Sci Bull 42(8): 684-689]. ( 2) No net loss of D1 protein occurred after strong light treatment. (3) Lin comycin taken up through petioles following strong light treatment had no s ignificant effect on D1 protein level and the decay of F-o in the dark. (4) Far-red light applied after strong light treatment could largely attenuate the increase in F-o and accelerate F-o decay in the dark. Based on these r esults, it is deduced that the increase in F-o under strong light is mainly due to reversible inactivation of part of PS II reaction centers, rather t han the net loss of D1 protein and that reversible inactivation of PS II is prevalent in some plants.