Abstract: [Objective]The objective of the present study was to reveal the relationship between sugar accumulation and the activity of sucrose-metabolizing enzymes in different Jujube cultivars and different parts of fruits at different developmental stages so as to provide a basis for further improving the sugar accumulation theory in jujube fruits.[Method] The fruits from three different cultivars, Ziziphus jujuba ‘Hupingzao’, Z. jujuba ‘Popozao’, and Z. jujuba ‘Pozao’, were used to determine the content of sucrose, fructose, glucose, starch and the relevant metabolizing enzyme activities in the shoulder and top part of jujube dates at different developmental stages with High Performance Liquid Chromatography (HPLC).[Result] 1) The sugar accumulation started a little earlier in shoulder part than in top part of dates of all three jujube cultivars. The content of soluble sugar in the fruit shoulder was significantly higher than that in the fruit top in all three jujube cultivars (P<0.05). Both fructose and glucose were mainly accumulated at early stage of fruit development, and the content of sucrose was very low in all tested cultivars. Cultivar ‘Hupingzao’ firstly began to accumulate sucrose, and the content of sucrose reached to 3-4 times greater than that of fructose and glucose at maturity. As for cultivar ‘Popozao’, the sugar accumulation pattern was similar to that of ‘Hupingzao’, while the sucrose accumulation in ‘Pozao’ was lastly occurred, and the content of fructose and glucose was much higher than that of sucrose. The soluble sugar content of ‘Popozao’ was significantly higher than ‘Hupingzao’ and ‘Pozao’ at fruit ripening stage(P<0.01). 2) The starch content of jujube fruits in all three cultivars was low over the whole developmental stage(the highest value was 6.78 mg·g^-1FW), and it was lower in shoulder than in top part. The activity of amylase in three cultivars showed opposite trend to that of starch accumulation throughout the process. 3) The metabolizing enzymes of sugar in stem end showed similar activities to that in calyx end in all three cultivars. The acid invertase(AI) activity was always higher than that of neutral invertase (NI). Highly active invertase promoted the metabolism of sucrose at the early stage of fruit development. The activity variation of sucrose phosphate synthase (SPS) was consistent with the change of sucrose accumulation in all varieties. The activities of sucrose synthase in direction of synthetic (SSs) in ‘Popozao’ and ‘Hupingzao’ were significantly higher than ‘Pozao’. The sucrose synthase activity in direction of cleavage (SSd) in three cultivars was low, and no significant difference was detected among different cultivars.[Conclusion]The jujubes of ‘Hupingzao’ and ‘Popozao’ were typically sucrose accumulated fruits, while ‘Pozao’ jujube was hexose-prevalent type. SPS regulated sugar accumulation in ‘Popozao’ fruits, and was also the common key enzyme to control fruit sucrose accumulation of all three cultivars, therefore it could be the main factor of different content of soluble sugar in different cultivars. The sucrose synthase (SSs) enzyme played a key role mainly in the synthetic direction during the course of fruit development. The fruit sugar accumulation of ‘Hupingzao’ was regulated comprehensively by sucrose metabolizing enzymes. Sugar accumulation in ‘Pozao’ fruit was regulated by both SSd and SPS, and amylase played an important role in the starch accumulation in jujube fruits for all three cultivars.

Key words: Ziziphus jujuba ‘Hupingzao’, Z. jujuba ‘Popozao’, Z.jujuba ‘Pozao’, fruit, sugar content, sucrose metabolizing enzymes