Assimilation of 15NH3 by Root Nodules Detached from Soybean Plants

The assimilation of ¹⁵NH₃ by crude breis prepared from crushedsoybean nodules was examined. The highest enrichment during60 min of reaction time with ¹⁵N was found in alanine and thenext highest in the amide-N of asparagine and glutamate. Thelabelling of allantoic acid was relatively low, although itwas higher than that of other amino compounds. Nodule breiswere separated into a bacteroid fraction and a supernatant plantfraction, and the ¹⁵NH₃ incorporation into the main nitrogencompounds by each fraction was determined. The bacteroid fractionwas much more efficient in converting ¹⁵NH₃ into glutamate,alanine and glycine than the supernatant fraction, while forallantoic acid, the supernatant fraction showed a greater ability.The incorporation of ¹⁵NH₃ into allantoic acid was stronglyinhibited by the addition of azaserine or allopurinol, and enhancedby organic acid compounds, especially fumarate, succinate andmalate. The mode of ureide formation in the course of ammoniaassimilation in the soybean nodule is discussed. ¹Present address: Department of Pharmacology, Nara Medical University,Kashihara, Nara 634, Japan. (Received February 2, 1981; Accepted May 16, 1981)