, Volume 61, Issue 3, pp 269-280

Light-induced increase in initial chlorophyll fluorescence Fo level and the reversible inactivation of PS II reaction centers in soybean leaves

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With a portable PAM-2000 fluorometer it was observed that responses of initial chlorophyll fluorescence Fo level to strong light were different in various plant species examined. When the photochemical efficiency of Photosystem II, Fv/Fm, declined, Fo increased significantly in leaves of some plants such as soybean and cotton, while Fo decreased remarkably in other plants such as wheat and barley. In order to explore the mechanism of the increase in Fo in soybean leaves, the change in D1 protein amount and effects of lincomycin and far-red light on these fluorescence parameters were observed by SDS–PAGE combined with gel scanning and chlorophyll fluorescence analysis. The following results were obtained. (1) The amount of inactive PS II reaction centers increased under strong light and decreased during subsequent 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) Lincomycin taken up through petioles following strong light treatment had no significant effect on D1 protein level and the decay of Fo in the dark. (4) Far-red light applied after strong light treatment could largely attenuate the increase in Fo and accelerate Fo decay in the dark. Based on these results, it is deduced that the increase in Fo under strong light is mainly due to reversible inactivation of part of PS II reaction centers, rather than the net loss of D1 protein and that reversible inactivation of PS II is prevalent in some plants.