Initial organic products of fixation of dinitrogen by root nodules of soybean (Glycine max)

When detached soybean Glycine max (L.) Merr. cv. Hark, nodules assimilate $[{}^{13}\text{N}]\text{N}_{2}$, the initial organic product of fixation is glutamine; glutamate becomes more highly radioactive than glutamine within 1 minute; ^{13}\text{N}$ in alanine becomes detectable at 1 minute of fixation and increases rapidly between 1 and 2 minutes. After 15 minutes of fixation, the major ^{13}\text{N}$-labeled organic products in both detached and attached nodules are glutamate and alanine, plus, in the case of attached nodules, an unidentified substance, whereas [^{13}\text{N}$]glutamine comprises only a small fraction of organic ^{13}\text{N}$, and very little ^{13}\text{N}$ is detected in asparagine. The fixation of $[{}^{13}\text{N}]\text{N}_{2}$ into organic products was inhibited more than 99% by C2H2 (10%, v/v). The results support the idea that the glutamine synthetase-glutamate synthase pathway is the primary route for assimilation of fixed nitrogen in soybean nodules.