Abstract:‘Fuji’ and ‘Golden Delicious’ apple fruits were taken as material to study the sugar metabolism and the key enzyme gene expression during fruit softening and how they were affected by cold storage or ethylene treatment. The results indicated that the starch content and amylase (AM) activity showed the most significant changes between ‘Fuji’ and ‘Golden Delicious’ and were dramatically regulated by low temperature and ethylene. Accordingly, the expression of MdAM was significantly promoted by the treatment of 2 mL/L ethephon while inhibited by 0.5 μL/L 1-MCP treatment at the late stage of storage in ‘Fuji’ fruit or at the early stage of storage in ‘Golden Delicious’ fruit. Meanwhile the expression of MdAM was significantly inhibited under 0 ℃ storage in both cultivars. This suggest that post-harvest starch degradation involved in apple fruit softening and are significantly affected by cold storage and ethylene treatment. Among the soluble sugars, the sucrose content increased clearly and was significantly subjected to the regulation by ethylene and low temperature, and the SPS had much stronger effect on sugar metabolism in post-harvest apple fruit than those of SS and AI. The SPS activity and the expression of MdSPS were significantly promoted by ethephon treatment and inhibited by 1-MCP treatment in ‘Golden Delicious’ fruit. This phenomenon was stronger than that in ‘Fuji’ fruit during storage. Less variation was observed on the fruit sugars content and the enzyme activity under cold storage, and the expression of MdSPS was significantly inhibited. These indicated that sucrose accumulation and SPS may have more close correlation with fruit softening among the regulation of sugar metabolism.
