Comparative effects of app1ication of coated and non-coated urea in clayey and sandy paddy soi1 microcosms examined by the 15N tracer technique

Abstract

¹⁵N assimilation was studied in bacteroid and cytosol fractions of soybean nodules. In the first experiment, after exposing the intact nodules to ¹⁵N₂ for 5 min and 10 min, most of the fixed ¹⁵N was detected in cytosol fraction. In cytosol fraction, ¹⁵N content of glutamine was the highest and followed by glutamic acid, alanine, and allantoin in this sequence, whereas, in bacteroid fraction, glutamic acid showed the highest ¹⁵N content and alanine and glutamine followed. In the second experiment, ¹⁵N assimilation of various ¹⁵N-labeled compounds in the separated bacteroid and cytosol fractions was investigated. In the separated bacteroid fraction which was fed with ¹⁵NH₄, ¹⁵N was incorporated very rapidly into glutamic acid, alanine, and aspartic acid, but very slowly into glutamine.

From these results, it was suggested that most of the fixed ammonia was exported to cytosol and assimilated via glutamine synthetase to glutamine, then via glutamate synthase to glutamic acid, and from these compounds various nitrogenous compounds were formed, but in bacteroids glutamate dehydrogenase and alanine dehydrogenase played an important role in the assimilation of fixed ammonia though quantitatively the contribution to ammonia assimilation in nodules was much less compared with cytosol.