Comparative studies on the distribution of nitrogen in soybean plants supplied with N2and NO3- at the pod filling stage

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Abstract
The fate of nitrogen originating from N2 and NO3 - was investigated in the soybean plant at the pod filling stage in relation to the transport and utilization of soluble nitrogen constituents in various organs. Nitrogen fixed by the nodules was rapidly metabolized to allan-toin and transported to the pods. Then allantoin was metabolized to amino acids in the pod shells or seeds and utilized for seed development. In the last paper of this series, nitrogen originating from NO3 - was shown to be first incorporated into the proteins of the vegetative organs, then transferred to the pods. In this study the nitrogen originating from NO3 - was translocated to the pods mainly in the form of asparagine. The turn-over rate of allantoin as well as nitrate was very high in soybean plants, and only a small portion of these compounds was stored for a comparatively long period of time.