PATHWAYS LEADING TO THE FORMATION OF AMINO ACIDS AND AMIDES IN LEAVES

Abstract

C¹⁴-labelled substrates were supplied to leaves, and the labelling patterns in derived amino acids were examined. A new technique is described for the ninhydrin decarboxylation of amino acids separated on paper chromatograms, making use of the Dynacon electrometer. Succinate-1,4-C¹⁴, succinate-2,3-C¹⁴, pyruvate-1-C¹⁴, pyruvate-2-C¹⁴, pyruvate-3-C¹⁴, C¹⁴O₂, and glutamate-1-C¹⁴were supplied to wheat leaves, and the total C¹⁴and carboxyl-C¹⁴in alanine, aspartate, glutamate, asparagine, and glutamine were determined. The results indicated that the amino acids and amides were formed mainly from the corresponding Krebs cycle intermediates. Carbon entered the Krebs cycle mainly by decarboxylation of pyruvate, but partly by its carboxylation. Extensive cycling did not occur. Various other suggested pathways, including the conversion of succinate to glutamic acid via succinic semialdehyde and γ-aminobutyrate followed by carboxylation, did not occur.When glucose-UL-C¹⁴was supplied to pea or bean seedlings, the labelling pattern in alanine and glutamine indicated their derivation from glucose via glycolysis and Krebs cycle pathways. However, the pattern in asparagine indicated that it may have been formed from products of glyoxalate cycle.