Influence of sodium ion on heavy metal-induced inhibition of light-regulated proton efflux and active carbon uptake in the cyanobacterium Anabaena flos-aquae

The light-induced proton efflux and active carbon uptake are inhibited by mercury and cadmium ions in Anabaena flos-aquae. The inhibitory effects of these heavy metal ions are reversed by 40 mM concentration of sodium. Here we report that light-induced proton efflux is sodium-dependent which leads to a characteristic enhancement in the rate of photosynthetic oxygen generation and carbon fixation. A low concentration (10 μM) of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) significantly inhibited the rate of oxygen generation while 10 μM carbonyl cyanide-m-chlorophenylhydrazone (CCCP) completely blocked the oxygen generation activity in the organism. The chlorophyll-a fluorescence yield indicates that little fluorescence quenching occurred in the absence of sodium ion. Increasing the extracellular sodium ion accelerated both the initial rate and the extent of fluorescence quenching. These results support the assumption that metal-induced inhibition of the photosynthetic machinery may be mediated by the movement of protons.