Inhibiton of the Photosystem II Photoactivation Process in Flashed Leaves by Sulfate

Summary The appearance of variable fluorescence with photoactivation was inhibited after sulfate infiltration in flash-grown leaves. The inhibition of the photoactivation by the treatment with sodium sulfate was also suggested by an investigation of the fluorescence emission spectra of the leaves: the change in the emission maximum that occurs along with the photoactivation was also inhibited by the sodium sulfate treatment. The effect of sodium sulfate was not due to its competition with chloride salts in photosystem II. Moreover, the infiltration of chloride salts (without sulfate) was also effective in inhibiting photoactivation, while sucrose infiltration had no effect. We propose that an excess of sodium sulfate promotes the inhibition of photosystem II photoactivation in leaves through the modification of the ionic balance in chloroplasts.