Bicarbonate effects on photo-inhibition. Including an explanation for the sensitivity to photo-inhibition under anaerobic conditions.

Isolated thylakoid membranes were found to be efficiently protected against photo-inhibition by sodium bicarbonate (20 mM NaHCO3) under both anaerobic and aerobic conditions. Furthermore, data are presented which indicate that the pronounced sensitivity to photo-inhibition under anaerobic compared to aerobic conditions is due to the removal of protecting bicarbonate, rather than oxygen, from the medium. A second type of bicarbonate effect on photo-inhibition, in apparent contradiction to the protective effect of added NaHCO3, is that thylakoid membranes that were depleted in their endogenous bicarbonate by treatment with formate were found to be less susceptible to photo-inhibition than thylakoids in the normal non-depleted state.