Abstract: The fruits of‘Fuji’and‘Golden Delicious’apple were taken as materials to investigate the changes of the soluble sugars and starch contents and metabolism-related enzymes activities，and analyzed the expression level of the MdSPS and MdAM genes during fruit development and softening. The results indicated that the changes of starch content and amylase（AM）activity had significant correlation with firmness loss and show significant differences between‘Fuji’and‘Golden Delicious’fruits. AM activity significantly increased in‘Golden Delicious’with fruit softening，while it remained a relatively low activity in‘Fuji’fruit. These phenomena were consistent with the decrease of starch content in‘GoldenDelicious’and the low content of starch in‘Fuji’fruit. In addition，the expression level of MdAM gene increased rapidly in‘Golden Delicious’fruit during storage，being compared to that in‘Fuji’fruit. We also found that the changes of sucrose，fructose and glucose content were significantly correlated with the loss of fruit firmness during maturity，which excepted that the changes of sucrose content in‘Golden Delicious’fruit showed significantly negative correlation with fruit softening during storage. Sucrose Phosphate Synthase（SPS）activity was significantly correlated with firmness in‘Golden Delicious’，being accompanied with its higher expression level of MdSPS gene. Taken together，we concluded that starch degradation involved in fruit softening and had a close correlation with fruit storability，and SPS may play more important roles in sucrose metabolism during fruit softening in apple fruits and was also correlated with fruit storable characteristics.

Key words: apple, fruit, development, texture softening, sugar, starch, metabolism, gene expression