SELF-CONTROL of UPTAKE and ASSIMILATION of NITRATE NITROGEN by WHOLE PLANT.

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Uptake, transport and metabolism of nitrate heavy nitrogen had been studied in the rice or wheat young plants under the variation of medium nitrate concentration, light condition or temperature differential between root and shoot.In the rice plants transferred into high concentration medium, all assimilative paths and xylem transport of newly absorbed nitrogen were initially accelerated. But, xylem transport of amino acid nitrogen was repressed after 10-12hr of transferring, although it was highly accumulated in the roots. It was estimated that the repression was due to reduction of amino acid unloading from xylem in shoots, where high concentration of amino acid nitrogen was observed. In case of wheat plants, loading of nitrogen was estimated to be repressed before reduction of assimilative activities.In the late dark period, wheat plants gave higher rates of nitrate uptake and xylem transport into shoots than in early and middle dark period. But activity of nitrate reduction in that period was the lowest. In the light period, nitrate reduction process was not likely to restrict assimilation of it by the plants supplied 3 mM nitrate medium.In the wheat plants of which shoots exposed to the temperature higher than that of roots, protein synthesis in the shoots slightly increased comparing to the plants with no differential of shoot temperature. But uptake and transport of nitrogen were decreased and mismatching to it. The nitrogen transport to shoots was the most sensitive process to the lower differential of shoot temperature, and was decreased by it.