Proline accumulation in Cylindrospermum sp.

The response of nitrogen fixing cyanobacterium Cylindrospermum sp. to 50 and 100 mM NaCl for 4 days was investigated. NaCl treatment resulted in a decrease of growth, chlorophyll content and PS II activity but increased the H2O2 and proline levels, electrolyte leakage and lipid peroxidation. Similar results were also obtained following UV-B exposure for 15 and 60 min (0.18 and 0.72 kJ m−2, respectively). Simultaneous exposure to UV-B and NaCl produced an additive effect on peroxide, MDA and proline accumulation. However, NaCl pre-exposure decreased H2O2 accumulation, lipid peroxidation and electrolyte leakage considerably. Similar results were obtained when the cyanobacterial cells were exogenously supplied with proline, and subsequently exposed to UV-B. These results strongly suggest a possible role of proline accumulated under salt stress conditions for the observed tolerance of Cylindrospermum sp. to UV-B radiation.