The incorporation of nitrogen into products of recent photosynthesis in Anabaena cylindrica Lemm.

In vivo tracer studies with 14C have been performed to help determine pathways of incorporation of newly assimilated nitrogen into N2-fixing cells of Anabaena cylindrica. After photosynthesis in Ar: O2:14CO2 for 30 min, the addition of N2 or NH+4 resulted in increased rates of 14CO2-incorporation both in the light and dark, and in increased incorporation of 14C into amino acids at the expense of sucrose and sugar phosphates. Evidence of enhanced sucrose catabolism and increased pyruvate kinase activity was obtained on adding nitrogen, and, of the 14C-labelling entering the tricarboxylic acid cycle, more appeared in citrate and 2-oxoglutarate than in malate and oxaloacetate. The kinetics of 14C-incorporation into various amino acids suggest that in the light and dark the most important route of primary ammonia assimilation involves glutamine synthetase and that glutamate, aspartate, glycine and probably alanine are formed secondarily from glutamine.