An investigation was made to study the assimilation and transport of15N-labelled nitrate nitrogen in rice plant (Oryza sativaL.). Nitrogen from labelled nitrate at the end of plant feeding was found mainly in nitrate form, and was more prevalent in roots, stem and leaf sheaths. The nitrite fraction had the next largest15N enrichment. The15NO3assimilation in the newly emerged panicle was mainly in amide and amino acid.The15N-incorporation at day 0 was greatest in amino acid and nitrate of roots and decreased towards the stem and leaves. Incorporation in these fractions considerably decreased from day 0 to day 10. Probably most of the nitrogen from the nitrate source was transported from the roots to the shoot in nitrate and amino acid forms.A decrease of15N-incorporation in the soluble N fraction and increase in the insoluble N fraction from day 0 to day 10 in plant parts, particularly the blades, suggested that protein synthesis occurred mostly in young parts of the shoot during this period. The marked variation in15N distribution in different parts of the plant during the 10 days indicated that the nitrogen in roots and tillers was probably remobilized and transported to other parts, particularly the upper leaf blades.Ammonium and nitrate nitrogen transport in rice plant are compared.
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