Influence of osmotic and metal stresses on nitrogenase activity of cyanobacteria ysolated from paddy fields

Samples were collected from paddy fields in Corum-Turk.ye. Nitrogen-free BG-11 medium was used for isolation of nitrogen fixing cyanobacteria. Acetylene reduction technique was used to determine the effects of different chemical agents on the nitrogenase activities of the cyanobacteria, which were identified at the genus level. Nostoc showed the highest nitrogenase activity (0.09 ethylene êl/mg.h) at 50 mM salt concentration. At 60 mM sucrose concentration, Nostoc showed the highest nitrogenase activity (0.08 ethylene êl/mg.h). The highest tolerances for the metals were present in Anabaena (0.006 ethylene êl/mg.h) for iron (20 ppm), Nodularia 0.1 ethylene êl/mg.h (for manganese 20 ppm) and Nostoc 0.96 ethylene êl/mg.h (for zinc 5 ppm) .