Comparisons of Ascorbic Acid Contents and Activities of Metabolism Relative Enzymes in Apple Leaves of Various Ages

Ascorbic acid(AsA)metabolism, including AsA content, metabolism relative enzymes activities and relationships among them, was investigated in leaves of apple (Malus domestica Borkh. 'Gala’) of various ages, i.e. young leaves, expanding leaves, mature leaves, aged leaves. The results showed that total AsA content and AsA content changed accordingly,reaching maximum in mature leaves and minimum in aged leaves, and changes of GalLDH activity were accordant with AsA content. With the decline of APX activities and accumulation of H2O2, the activities of MDHAR, DHAR and GR which conduce to regeneration of AsA were lowest at aged leaves,so as to the extent of AsA oxidation reached maximum in aged leaves.