Some Effects of Sodium on Nitrate Assimilation and N(2) Fixation in Anabaena cylindrica

Abstract

Anabaena cylindrica grown with nitrate required higher levels of sodium (0.4 meq/l NaCl) to prevent chlorosis than when grown without combined nitrogen (0.004 meq/l NaCl). Nitrite accumulated in sodium-deficient cultures containing nitrate. Amounts of nitrite similar to those found in deficient cultures when added to normal cultures resulted in a chlorosis of the cells. Thus loss of chlorophyll was caused by nitrite toxicity.A deficiency of sodium resulted in an increased incorporation of (15)NO(3), (15)NO(2), (15)NH(3) or (14)C glutamate into protein compared with normal cells. The enzyme nitrate reductase was markedly increased in cells grown without sodium.Evidence from chloramphenicol treatment of the cells suggests that sodium may exert its control of nitrate reductase through a protein factor(s).By contrast, N(2) fixation was reduced in sodium deficient cells. Since the incorporation of ammonia or glutamate into protein was increased under these conditions, it is likely that the element is required for the conversion of N(2) gas into ammonia. Various nitrogenous compounds including ammonium chloride, amides and amino acids at low concentrations (0.1 mm) greatly reduced the nitrite accumulation in sodium-deficient cultures.