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

The light-induced proton efflux and active carbon uptake are inhibited by m ercury and cadmium ions in Anabaena flos-aquae. The inhibitory effects of t hese heavy metal ions are reversed by 40 mM concentration of sodium. Here w e report that light-induced proton efflux is sodium-dependent which leads t o a characteristic enhancement in the rate of photosynthetic oxygen generat ion and carbon fixation. A low concentration (10 muM) of 3-(3,4-dichlorophe nyl)-1,1-dimethylurea (DCMU) significantly inhibited the rate of oxygen gen eration while 10 muM carbonyl cyanide-m-chlorophenylhydrazone (CCCP) comple tely blocked the oxygen generation activity in the organism. The chlorophyl l-a fluorescence yield indicates that little fluorescence quenching occurre d in the absence of sodium ion. Increasing the extracellular sodium ion acc elerated both the initial rate and the extent of fluorescence quenching. Th ese results support the assumption that metal-induced inhibition of the pho tosynthetic machinery may be mediated by the movement of protons.