Correlation between immuno-gold labels and activities of the cytochrome-c oxidase (aa₃-type) in membranes of salt stressed cyanobactria

Abstract

Anacystis nidulans (Synechococcus PCC6301) and Synechocystis PCC6803 were grown photoautotrophically in a turbidostatically operated chemostat at a constant cell concentration of 2.05:0.3 ~1 packed cell mass per ml in the presence of elevated NaC1 concentrations up to 0.5 M ('salt stress'). The impact of salt stress on cytochrome-c oxidase (EC 1.9.3.1) was studied on isolated and purified membranes, and by immuno-gold labeling of thin-sectioned whole cells ATPase activities of membranes isolated and separated from cells under varying salt stress were also measured. Anacystis and Synechocystis adapted to the presence of 0.5 M NaC1 in the medium with lag phases of 2 days and 2 hours, respectively. Both isolated plasma and thylakoid membranes from salt adapted Synechocystis displayed 5-to 8-times enhanced cytochrome-c oxidase activities while in Anacystis the effect was restricted to the plasma membrane. In either case less than proportionately increased counts of immuno-gold labeled cytochrome-c oxidase molecules in the respective membranes were obtained, the additional increment being attributed to the increased lipid content of the membranes from salt-adapted cells, leading to increased specific activities of the enzyme compared to control cells. ATPase activity of plasma membranes from Synechocystis was far more increased than of those from Anacystis while in thylakoid membranes the differentiating effect was less pronounced. Our results are discussed in terms of distinct strategies for salt adaptation in the two cyanobacterial species whereby in Anacystis the plasma membrane-bound respiratory chain and in Synechocystis the plasma membrane-bound ATPase(s) play the major role for plasma membrane energization which, in turn, is necessary for the active exclusion of sodium from the cell interior.