| Pumpkin was planted not less than any other vegetable crops in our country. Its nutrition value and medical healthe function are very high. And playing an important action at improving people's bite and sup habit, even at changing our meal configuration. However, the poor quality of pumpkin fruits give rise to a great reduction in the economic benefit. With the development of economic internationalization, the market of pumpkin will face competition internationalization. So it is very urgent to improve the quality of pumpkin fruits. With the increasing living standard and the regarding of the health,there is a large demand for higher quality pumpkin fruits. sugar, starch andβ-Carotene contents are mainly guide line of the quality of pumpkin fruits,especially the contents of sugar. Because it affects the tastes and color of fruit and serve as a precursor as well for synthesis of organic acid, vitamin and carotenoids. Therefore, it is very imperative to study the mechanism of sugar accumulation for the ultimate goal of improving the quality of pumpkin.Three pumpkin varieties were used as research materials. The genotypic difference in sugar-accumulating patterns and its related sucrose metabolizing enzymes were systemically analyzed for elucidating the physiological aspects that are possibly responsible for the difference. The main results were as follows:By comparing three pumpkin genotypes, the result showed that the contents of the nutrition elements increasing were different at different growth stage with the"hongxiangli"fruits growing. At early stage dissolubility sugar was the main accumulation. Evening is the stage of accumulation of starch."huanglang"accumulate total sugar main at evening. Starch accumulate through the developing fruit of"huanglang". Starch was the main accumulation at early stage of the developing fruit of"miben". Evening is the accumulation stage of sugar. According to Fructose×2+Glucose×1+Sucrose×1.45+Pentose×1.52, the sweetness index of"miben"was the highest at maturity. The sweetness index of"miben"was 184.21 and the sweetness index of"huanglang"was 153.84. meanwhile it was 115.90 in"hongxiangli". The contribution ration of fructose to sweetness index were 54.2% and 42.0% in"hongxiangli"and"huanglang", meanwhile it was 42.8% in"miben". These findings suggested that the fructose level was the main determinant of sweetness in different genotypic pumpkin. Pumpkin of"hongxiangli"mainly accumulated starch.Cumulation ofβ-Carotene were varied in three pumpkin varieties. But all of their current were increase mainly, the biggest increse extent is"hongxiangli"in the there varieties, especially during 5～6 weeks, at this stage the accumulation ofβ-Carotene count for 70℅ in this developmental stage, while the cumulation of"huanglang"was slowly in this developmental stage, and was the lowest. It depends on the developmental stage ofβ-Carotene cumulation in"miben", it continue increased at early stage, during 6～7 weeks its change was not evidently and retained at 11.0 mg/100 g·FW, even reduce more or less, but it rised at 17.7 mg/100 g·FW sharply. So we knowed that"hongxiangli"was a variety ofβ-Carotene accumulation.After pollination, glucose and fructose were the predominant soluble sugars detected in flesh of pumpkin before sucrose accumulation."miben"and"huanglang"had no apparent differences in contents and had very similar accumulating patterns. The accumulation of sucrose occurred in mid-stages and latter-stages of fruit development. The genotype with high sucrose"miben"pumpkin accumulation had much intensive and faster sucrose accumulation with much higher sucrose content at maturity."hongxiangli"had much intensive and faster starch accumulation, and was superior in starch accumulation.In early stage of fruit development, the sucrose cleavage enzymes behaved much higher activities than sucrose synthetic enzymes. The net activities between synthesis and cleavage had higher negative value. The photosynthetic substances translocated were decomposed, consumed and utilized, and the rate for sucrose accumulation was slower. In late developmental stage, the sucrose was quickly accumulated as a result of the sucrose cleavage enzymes behaved lower activities than sucrose synthetic enzymes at this stage, and they got balance till mature. In the present investigation, there was no or synthesis very low sucrose accumulation when the net activities was negative. After net activities was changed to positive, sucrose accumulation was enhanced.Sucrose accumulation coincided with the sucrose phosphate synthase activity and sucrose synthase activity in"hongxiangli"pumpkin. Sucrose accumulation increased with the hoist of sucrose phosphate synthase activity and sucrose synthase. There was higher invertase activities in early developing fruits in"miben"and"huanglang", which gave rise to higher hexose contents in flesh. Hexose was the carbon source for vigorous growing tissues. Moreover, high hexose level was essential to maintain high osmotic pressure in cell and ensure sufficient water imbibition in early stage. At mid-stages, sucrose accumulation coincided with the hoist of sucrose phosphate synthase activity and sucrose synthase activity in"huanglang"and"miben"pumpkin. A reduction in acid invertase, would be a prerequisite for sucrose accumulation at latter-stages.The genotype with high starch"hongxiangli"accumulation had no relationship with starch phosphorylase, and coincided with the sucrose synthase activity."miben"starch accumulation had the similar starch-accumulating patterns with"hongxiangli"at early stage. In latter developmental stage of"huanglang", the starch was quickly accumulated as a result of the hoist of starch phosphorylase at this stage.According to our study, we thought that the sucrose accumulation in fruit due to both the high sucrose phosphate synthase and sucrose synthase activity and low invertase activity. Sucrose synthase acted an important role at starch accumulation in high-starch accumulation fruit, starch phosphorylase caused starch accumulation in low-starch accumulation fruit.
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