Effect of salinity on some physiological and biochemical responses in the cyanobacterium Synechococcus elongatus

In this study, some physiological and biochemical responses of Synechococcus elongatus to salt stress were investigated. The cyanobactrium was grown in BG-11 medium under different concentrations of NaCl (0, 0.5, 1 M). The results indicated that the growth of S. elongatus was significantly inhibited under salt stress on days 5, 9 and 12 after treatment. Protein content increased in S. elongatus on day 12 in presence of salt. Salinity induced proline accumulation at 1 M NaCl on day 12 and caused a significant increase in hydrogen peroxide content on day 5. Catalase (CAT) activity continuously increased on day 5. An increasing trend in polyphenol oxidase (PPO) activity was indicated on days 5 and 9. Superoxide dismutase (SOD) activity gradually induced with increasing NaCl concentrations on day 5. Salt stress decreased chlorophyll content compared to that of control in three stages of growth, and carotenoid content declined on days 9 and 12. The contents of phycobiliprotein (PBP), phycoerythrin (PE) and phycocyanin (PC) enhanced significantly under different NaCl concentrations on days 5 and 9. These results show that S. elongatus has limited adaptive potential to salinity, and the optimum medium for its culture should not bear NaCl even at a moderate level, if production of carotenoids is aimed.