NITROGEN ABSORPTION BY PLANT-ROOT FROM THE CULTURE-MEDIUM WHERE ORGANIC AND INORGANIC NITROGEN COEXIST .2. WHICH NITROGEN IS PREFERENTIALLY ABSORBED AMONG [U-C-14]GLUNH2, [2,3-H-13]ARG AND NA15NO3

The investigation was done to clarify which N compounds, organic or inorganic, were preferentially absorbed by the root from the medium where they coexist. The plants, pretreated with NO3 10 days after depletion of seed nutrients, were treated with 3 mixed N compounds, 15N-NO3, [2,3-3H]Arg and [U14C]GluNH2 [glutamine], at the same concentration of 10 ppm N. The treatment conditions consist of light (6000 lux) or darkness and high (20.degree. C) or low (4-5.degree. C) medium temperature. Under high temperature condition, N absorption was in the following order: GluNH2-N > Arg-N > NO3-N under both light and dark conditions. Under low temperature condition, the order became Arg-N > GluNH2-N > NO3-N. Arg was the least susceptible to low temperature treatment. The plant absorbed organic N preferentially to inorganic one. GluNH2 was supplied to the plant in the form of [G-3H]-GluNH2. It was quickly metabolized as a good N source. Apparently barley plants absorb some organic N preferentially to inorganic ones.