The functional state of PS II in the leaves of wheat seedlings subjected to the complex action of Co2+ and photoinhibition was determined on the basis of various characteristics of the delayed fluorescence of chlorophyll a (msec DF Chl a ). The effect of Co2+ was expressed in a sharp decrease in the characteristic value of msec DF Chl a of the PS II reaction center and in a weaker blocking of the donor side characterizing the state of the Mn4O5Ca cluster and Yя . Reactive oxygen species (ROS) generated during photoinhibition also blocked to a greater extent the acceptor side of the PS II ETC. An increase in the adaptation time was observed a significant drop in activity on the donor side of the ETC PS II. The combined effect of both factors had little effect on the change in fluorescence characteristics, which remained almost at the level of the effect of Co2+. It has been shown that the adaptive capabilities of photochemical reactions occurring in the ETC of PS II under complex stress are stimulated by the low molecular weight antioxidant Na-ascorbate. It is assumed that Na-asc plays a decisive role in protecting chloroplasts from oxidative stress by quenching O2 ¯ and *OH1.
PS II, ETC, Со2+, photoinhibition, ROS, Na-ascorbate
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