Abstract: 【Objective】The aim of this work is to study difference in starch accumulation between high- and low-starch- accumulating cultivars and characterization of sugar metabolism during fruit development, and to identify the related enzymes activities in order to provide a theoretical guidance for increasing fruit sugar content and improving flavour and quality of fruit.【Method】High-starch-accumulating variety ‘Hongyang’ and low-starch-accumulating variety ‘White’ were used to measure the changes in fruit relative growth rate (RGR), carbohydrate content (starch, glucose, fructose and sucrose), dry matter and enzyme activity in relation to carbohydrate metabolism throughout the growing season.【Result】The carbohydrate concentration was negatively correlated with fruit relative growth rate, and constantly increased with starch accumulation. The starch content was positively correlated with the soluble sugar contents (glucose, fructose and sucrose) and dry matter, and the ratios of maximum starch content to carbohydrates in ‘White’ and ‘Hongyang’ fruit were 87.1% and 84.1%, respectively. The higher rate of starch accumulation, which was also maintained for a longer period of time, was found in ‘Hongyang’, and the starch peak was much higher in ‘Hongyang’ than in ‘White’. The rate of starch accumulation and the maximum starch content in ‘Hongyang’ were 0.685 mg•g-1FW•d-1 and 70.78 mg•g-1FW, and they were 1.34 and 1.69 fold higher than those in ‘White’, respectively. The period of starch accumulation of ‘Hongyang’ was 21 days longer than that of ‘White’. When starch content in ‘White’ fruit rapidly dropped, starch accumulation of ‘Hongyang’ fruit linearly increased. As a consequence, the higher level of starch concentration in ‘Hongyang’ fruit maintained until harvest, while almost all starch in ‘White’ had been converted into soluble sugars prior to harvest. Neutral invertase (NI) and acid invertase (AI) activities were consistently much higher in ‘white’ than in ‘Hongyang’. In contrast, ADP-glucose pyrophosphorylase (AGPase) and sucrose phosphate synthase (SPS) activity was always stronger in ‘Hongyang’ than in ‘White’. Fruit starch content was positively and significantly correlated with AGPase and SPS activities, but was negatively and strongly correlated with NI and AI activities. NI activity was positively and significantly correlated with NI activity, while was negatively correlated with the activities of AGPase, SPS, sucrose synthase (SS), fructokinase (FK), glucokinase (GK) and UDP-glucose pyrophosphorylase (UGPase). AGPase activity in ‘Hongyang’ had positive and significant correlation with the activities of SPS, SS, FK, GK and UGPase.【Conclusion】Kiwi fruit accumulated carbohydrate predominantly as starch. AGPase was a determinant of high starch concentration in fruit, in addition to this, the variation of NI, AI and SPS activity may be the causes of high or low contents of starch, dry matter and soluble sugars in fruit.

Key words: kiwi fruit , fruit development , starch , sugar metabolism