Ammonia Assimilation and Excretion in an Asymbiotic Strain of Anabaena azollae from Azolla filiculoides Lam.

One independent, asymbiotic strain of Anabaena azollae isolated irom Azolla filiculoides Lam. was examined with respect to ammonia «uptake», assimilation, and excretion. Extracellular release of ammonia was initiated by adding L-methionine-D,L-sulfoximine (MSX). NH₃-grown cells removed newly added ammonium from the medium faster (25.2 to 19.7nmol min⁻¹ mg⁻¹ protein), liberated ammonia more slowly (0.33 to 0.63 μmol h⁻¹ mg⁻¹ protein), and possessed lower glutamine synthetase (GS) transferase activity (55%) than the N₂-grown cells. GS was always still partially active (20–40 % of uninhibited control) in A. azollae when excretion commenced. Uninhibited GS activity was lower than that of Anabaena sp. 7120. No optimum was observed between pH 5 and 9 for ammonia movement into or out of cells of A. azollae.