SYNTHESIS OF AMINO ACIDS AND PROTEINS IN BARLEY SEEDLINGS

Abstract

A study has been made of the assimilation of ammonium salts by young barley seedlings grown under controlled conditions in water culture. The synthesis of amino acids, amides and proteins in the roots was traced by means of isotopic labelling with 15N. Chromatographic analysis on ion‐exchange resins was used to separate the free and combined amino acids of the root tissues. There was evidence of the synthesis of proteins in the roots under the experimental conditions. After short periods of assimilation, the soluble amides and amino acids, especially glutamine and glutamic acid, were highly labelled with 15N, indicating a rapid synthesis of these constituents. Subsequently, the abundance of 15N in the amino acids combined in the root proteins showed a marked increase. The data are consistent with the occurrence of an extensive synthesis and interconversion of amino acids and their utilization as precursors in the synthesis of proteins. The importance of glutamic acid and glutamine in the assimilation of nitrogen and synthesis of amino acids is shown by the rapid incorporation of 15N into both the amide and amino groups. Other amino acids are more slowly labelled and may be formed secondarily by transamination or interconversion. γ‐Aminobutyric acid appears to play a significant part in the metabolism of the roots, since it is formed at an early stage of assimilation. The labelling of γ‐aminobutyric acid with 15N indicates that, in barley seedlings, it is a secondary product, rather than a precursor of glutamic acid or glutamine. Copyright © 1961, Wiley Blackwell. All rights reserved