Metabolism of Carbon‐14 Labelled Arginine, Citrulline and Ornithine in Intact Apple Stems

Abstract A study was made of the absorption and metabolism of arginine‐guanido‐14C, citrulline‐carbamyl‐14C and ornithine 1‐14C which had been applied to apple stem internodes by a perfusion technique at intervals throughout the year. The results showed that these amino acids were interconverted according to the Krebs‐Henseleit cycle always in the direction arginine‐ornithine‐citrulline‐arginine. In addition ornithine was degraded by another pathway with loss of CO2. This loss was particularly extensive during the period June to August when labelled proline and glutamic acid were also found. The evidence is consistent with the initial breakdown of ornithine taking place via glutamic semi‐aldehyde.