EFFECT OF CHROMIUM(VI) ON PHOTOSYSTEM II ACTIVITY AND HETEROGENEITY OF SYNECHOCYSTIS SP. (CYANOPHYTA): STUDIED WITH IN VIVO CHLOROPHYLL FLUORESCENCE TESTS(1).

Abstract

The inhibitory effect of Cr(VI) on the PSII of Synechocystis sp. was studied. Cr(VI) reduced O2 evolution and inhibited the water-splitting system in PSII. S-states test and flash induction test showed that Cr(VI) exposure increased the proportion of inactivated PSII (PSIIX ) and PSIIβ reaction centers, which increased the fluxes of dissipated energy. JIP test and QA (-) reoxidation test demonstrated that Cr(VI) treatment induces inhibition of electron transport from QA (-) to QB /QB (-) and accumulation of P680 (+) . More QA (-) had to be oxidized through S2 (QA QB )(-) charge recombination and oxidation by PQ9 molecules in PSII under Cr(VI) stress. These changes finally decreased the index of photosynthesis performance.