INCORPORATION OF ^<15>N INTO VARIOUS NITROGENOUS COMPOUNDS IN INTACT SOYBEAN NODULES AFTER EXPOSURE TO ^<15>N_2 GAS

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The intact nodules attached to the upper part of soybean roots were exposed to ^<15>N_2,and the incorporation of ^<15>N into various soluble nitrogen constituents was investigated. Results indicated that ammonia, a primary product of N_2 fixation, was located in more than two compartments. Ammonia reduced from N_2 gas seemed to be incorporated firstly into glutamine especially amido-group nitrogen. Newly fixed nitrogen was secondly incorporated into glutamic acid and alanine in this sequence. These results suggested that fixed ammonia was assimilated by glutamine synthetase/glutamate synthase pathway. Turn-over rate of allantoin plus allantoic acid and serine was relatively high, although apparently these compounds were not primary products of newly fixed ammonia. ^<15>N content of allantoin was always higher than that of allantoic acid. ^<15>N incorporation to aspartic acid and asparagine was relatively slow, especially in early period. In bacteroid fraction there is much amount of ammonia comparing with other compounds, while allantoin and asparagine were presented exclusively in cytosol. ^<15>N was incorporated into nitrate within a few minutes especially in bacteroids.
一般社団法人日本土壌肥料学会の論文