Partitioning and metabolism of nitrogen supplied as nitrate, amides, and allantoin to detached vegetative shoots of soybeansviatranspiration stream

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Abstract
Primary partitioning and metabolism of nitrogen supplied as nitrate, amides, and al-lantoin in vegetative shoots of soybeans (Glycine max L. cv. Akisengoku) were studied by feeding the cut shoots with 15N-labeled substrates via the transpiration stream for 1 or 2 h under light conditions. Nitrate-N distributed to both growing and mature leaves intensively with little retention in the stem+petioles, while glutamine- and asparagine-N distributed relatively more actively to the growing leaves than to the mature leaves with a large retention in the stem+petioles. Allantoin-N showed a partition pattern intermediate between that of nitrate-N and amide-N. Nitrate-N was assimilated into amino acids in both growing and mature leaves more actively than amide-N of asparagine and allantoin-N. Glutamine synthesis may be operating in different compartments, chloroplasts and cytoplasm, through the utilization of the ammonia produced from nitrate and other sources, respectively. Asparagine synthesis was more active in mature leaves than in growing leaves, and in contrast the utilization of asparagine was more active in the growing leaves than in mature leaves. The amide-N of asparagine was transferred to the amide of glutamine followed by glutamic acid and alanine. AHantoin was synthesized using added nitrate and asparagine (amide) as the N source in both growing and mature leaves, and in contrast, the utilization of allantoin-N to form amino acids was very active in the growing leaves.