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Articles

Initial Organic Products of Fixation of [¹³N]Dinitrogen by Root Nodules of Soybean (Glycine max) ¹

Yael Avissar

Wan-Shen Chien

MSU-ERDA Plant Research Laboratory, Michigan State University, East Lansing, Michigan 48824, Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824, Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824

When detached soybean Glycine max (L.) Merr. cv. Hark, nodules assimilate [¹³N]N₂, the initial organic product of fixation is glutamine; glutamate becomes more highly radioactive than glutamine within 1 minute; ¹³N in alanine becoms detectable at 1 minute of fixation and increases rapidly between 1 and 2 minutes. After 15 minutes of fixation, the major ¹³N-labeled organic products in both detached and attached nodules are glutamate and alanine, plus, in the case of attached nodules, an unidentified substance, whereas [¹³N]glutamine comprises only a small fraction of organic ¹³N, and very little ¹³N is detected in asparagine. The fixation of [¹³N]N₂ 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.

³ To whom requests for reprints should be sent.

¹ This research was supported by the United States Energy Research and Development Administration under Contract EY-76-C-02-1338, and by the National Science Foundation. Y. A. was supported by National Science Foundation Grant PCM-76-22793 to K. D. Nadler. N. S. received partial support from the Deutsche Forschungsgemeinschaft.

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