Nitrate Reduction and Partitioning of Nitrogen in Komatsuna (Brassica campestris L. var. rapa) Plants : Compartmental Analysis in Combination with ^<15>N Tracer Experiments

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Komatsuna (Brassica campestris L. var. rapa cv. Misugi) is a leafy vegetable that readily accumulates nitrate in its tissues. Plants grown hydroponically with 2 mM nitrate in a greenhouse were fed ^<15>N-labeled nitrate for 2 h, followed with nonlabeled nitrate for 8 h. At intervals of 2 h, the plants were sampled and analyzed for the distribution of ^<15>N in the nitrate, amino acids, and proteins in the tissues of roots, petioles plus midribs, and leaves. Nitrate reduction and nitrogen fluxes were examined using a compartmental analysis with 19 compartments and 28 transfer rate constants. Nitrate existed in the three types of tissues as a large storage pool and a small metabolic pool. Nitrogen reduction was observed in these tissues, but mainly in the leaf tissue, Nitrate uptake and reduction rates were smaller in the dark than in light, and particularly nitrate reduction in the shoot was less in the dark. The rate of protein synthesis was much greater in the light. The simulation, using compartment models and ^<15>N distribution data, may be useful for estimating actual rates of nitrogen transport and metabolism in the whole plant system.
日本植物生理学会の論文