Effect of nitrate on nitrogen-fixation by the blue-green alga Anabaena cylindrica

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The effect of nitrate on nitrogen-fixation in the blue-green alga Anabaena cylindrica Lemm (Fogg strain) was investigated. At concentrations up to 2 × 10^<-2> M, nitrate neither inhibited the activity of nitrogenase nor repressed its formation. At the late logarithmic phase, more than 50% of cell nitrogen was provided by nitrogen-fixation when the cells were grown in the presence of nitrate. Ammonia at a concentration of 1 × 10^<-3> M completely repressed the formation of nitrogenase, but had no effect on its activity. Nitrogen-fixing activity in the alga varied to a considerable extent during growth on N_2 and the maximum activity was attained at the middle logarithmic phase. However, atmospheric nitrogen did not directly affect the induction of nitrogenase. The formation of nitrogenase in A. cylindrica appears to be controlled by the intracellular level of a certain nitrogenous metabolite.
日本植物生理学会の論文