Salinity-induced physiological and proteomic changes in Anabaena doliolum

This study is the first to offer information on salinity-induced inhibition of physiological variables, changes in proteome, and induction of glycolate metabolism in Anabaena doliolum. A significant reduction in O2-evolution, carbon fixation, chlorophyll and NADPH/NADH level and increase in intracellular Na+ and respiration were observed following 150 mM NaCl treatment for 1 and 24 h. Interestingly, ATP content registered significant decrease after 1 h and recovery after 24 h treatment of 150 mM NaCl. Two-dimensional gel electrophoresis and MALDI-TOF MS detected a set of six proteins showing significant reproducible alterations, and homology with iron superoxide dismutase, superoxide dismutase (imported), phycocyanin alpha chain, elongation factor-Tu (EF-Tu), ribulose 1,5-bisphosphate carboxylase/oxygenase and phosphoribulokinase of Nostoc PCC7120. Increased RuBisCO and decreased carbon fixation suggested operation of glycolate metabolism. This was confirmed by accumulation of free and phospho-glyceric acid, increase in glycolate oxidase activity, glycine, serine and ammonium contents. Since peroxide generated in this pathway cannot be scavenged due to sensitivity of catalase to NaCl the organism fails to acclimatize under salt stress.