Barleys were precuItured with organic nitrogen, inorganic nitrogen or with a combination of both, and the ability of the plant roots to absorb 15N-NO2was investigated. A. Plant was water-cultured for 50 days in the medium containing NO3, NO3:Arg(2:1), NO3:Arg(1:1), NO3:Arg(l:2), Arg or His as nitrogen source. 1) All the plant water-cultured in the medium containing Arg and also His showed better growth than those grown in NO3medium. 2) Pretreated plants with different nitrogen sources were introduced to 15N-N3, for 30 min. The newly absorbed nitrogen per dry matter of the root was the highest for the NO3pretreatment, and its value was in proportional to the NO3content in the pretreated medium. Pretreatment of His showed the same value as that of Arg. B. The plant, pretreated with NO3or Arg as the sole source of nitrogen, was treated with 15N-NO3or [ureido-15N]Arg for 30 min. 1) NO3-N was quickly metabolised into GluNH3> Glu>Ala and γ·AD in NO3pretreatment, but, NO3-N was scarcely metabolised into them in Arg pretreatment. 2) On the other hand, Arg[ureido]-N was easily absorbed and incorporated into amides and amino acids in both nitrogen treatments. C. It can be concluded that nitrogen metabolism in the plant root is closely related to the difference in nitrogen pretreatment (organic, inorganic or both), hence, the amounts and varieties of absorbed nitrogens by the root would be affected at the treatment time. © 1979 Taylor & Francis Group, LLC.
