Seasonal Variations in Absorption and Metabolism of Carbon‐14 Labelled Arginine in Intact Apple Stem Tissue

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Abstract
At intervals through the year a study was made of the absorption and metabolism of arginine‐C 14(U) which had been perfused into the wood of apple stem internodes. Absorption was greater during the period May to September than at any other time of the year. The metabolic breakdown of arginine took place only after absorption but the products found varied widely with season. From the analyses it is concluded that arginine is metabolized by the Krebs‐Henseleit cycle at all times of the year, in addition to which during the period from May to August there are other pathways in operation that result in a more extensive breakdown so that all the N in arginine becomes available for new growth.