Masashi Fukumoto

Seasonal changes of carbohydrates metabolism in apple trees

Abstract Apple tree ( Malus pumila Mill. var. domestica ‘Jonagold’) accumulated starch in roots and branches as a reserve carbohydrate. This accumulation of starch was observed to occur from July to November, while the amount of soluble carbohydrates in the roots and branches was relatively small and showed little variation. After November, accompanying the fall of temperature, the starch changed to soluble carbohydrates and accumulated, especially as sucrose, in these organs. In summer, when starch accumulated in the wood and bark tissues of 2-year-old branch sections, starch synthase activities decreased to half of those in winter, while the amylase activity decreased to one quarter. Consequently, the metabolism of starch appears to have been changed from degradation to synthesis, and starch may be accumulated in these tissues. In winter, the amylase, sucrose-6P synthase and sucrose synthase activities in the wood and bark tissues increased, changing the starch to glucose, fructose and sucrose. These soluble carbohydrates may play an important role in the cold- and frost-resistance of a tree in winter, as well as providing a supply of energy and substrates for the early growth of shoots in spring. When trees were grown in water culture with non-nitrogen fertilizer, the amylase, sucrose-6P synthase and sucrose synthase activities of the wood and bark tissues in branches were suppressed in comparison to control trees supplied with nitrogen fertilizer. Starch synthase activity in the bark tissue was also suppressed, but the wood tissue showed the same level as the control trees. Consequently, abundant starch accumulated in the wood tissue of trees grown in non-nitrogen fertilizer. This may indicate that wood tissues, by depositing starch, may play a role in keeping the balance of demand and supply in carbohydrates.