Relationship between the characteristics of sugar accumulation and fruit quality in apple (Malus domestica Borkh.) fruit.

The fruits of two apple cultivars,'Fuji' and 'Ralls',were used as materials to understand the effect of sugar accumulation and their metabolism on quality formation during fruit development.The results indicated that:(1)The fruit of two apple cultivars mainly accumulated hexoses (fructose and glucose),but there was significant difference in the sugar content and their proportion.During fruit development,the fructose accounted for the most proportion of soluble sugar in 'Fuji',the ratio of fructose and glucose (F/G) was 1.56.However,the highest soluble sugar in 'Ralls' was glucose,its F/G was only 0.68,no more than half of 'Fuji'.The contents of sucrose were at very low levels in both 'Fuji' and 'Ralls'.(2)The activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS) increased rapidly,while acid invertase (AI) activity increased slowly with soluble sugar accumulation in 'Fuji' apple,and the neutral invertase (NI) changed little.The analysis of correlation indicated that AI and SPS were most significantly related to sugar accumulation in 'Fuji' apple,and the role of SS mainly showed in late stage,no relation with NI.However,SPS had main role in sugar accumulation,and the roles of SS and NI mainly occurred in early stage.(3)The change of starch had a similar rule in both 'Fuji' and 'Ralls'.Their difference mainly occurred in late stage.After peaks of starch content,its degradation rate in 'Fuji' was faster and its content was lower than that of 'Ralls'.Meanwhile,the amylase activity in 'Fuji' was also higher than that in 'Ralls'.In the whole,there was remarkable difference in the sugars accumulation and starch degradation between 'Fuji' and 'Ralls',which directly or indirectly affected on fruit quality formation through their different sugar metabolism.