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

在中等硝酸盐浓度、光照条件和根冠温差条件下，研究了水稻和小麦幼苗对硝态氮的吸收、运输和代谢。在高浓度条件下，水稻植株的所有吸收途径和木质部运输都被加速。但是，氨基酸氮的木质部运输在10-12小时后被抑制，尽管它在根中高度积累。据估计，这种抑制是由于在氨基酸氮浓度较高的地上部减少了从木质部卸载的氨基酸所致。在小麦植株中，氮素负荷量在同化活性降低之前被抑制，在黑暗后期，小麦植株的硝酸盐吸收速率和木质部向地上部的运输速率高于黑暗早、中期。但这一时期的硝酸盐还原活性最低。在光照期间，硝酸盐还原过程不太可能限制硝酸盐被供应3 mM硝酸盐介质的植株同化。在地上部温度高于根部温度的小麦植株中，与没有地上部温度差异的植株相比，地上部蛋白质合成略有增加。但氮素的吸收和运输减少，并与之不匹配。氮素向地上部的运输是对地上部温差最敏感的过程，地上部温差降低了氮素向地上部的运输。

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.