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Melon is one of the important horticultural crops in the worldwide .China is the largest country of melon fruit production that accounted for more than 40 percent of total growing acreage and yield in the world. In order to improve quality of melon fruits ,fruits of three inbred lines HN-001,HN-002 and HN-004 were used as materials, they were carried out to study the changes of fruit growth dynamic and sugar contents and activities of enzymes related sugar metabolizing during developing melon fruits of mesocarp and placenta .The main findings were as follows:1 Melon fruit growth dynamic1) Fruits were sampled regularly after artificial pollination,the physical properties of melon fruits in developing were determinded, including weight, volume, color, vertical and horizontal diameter, firmness and total soluble solid content. It was found that the growth curves of weight and volume were single“S”in three inbred line melon fruits.The vertical and horizontal diameter increased rapidiy from 0 to 15 days after pollination,and then increased slowly.The growth rates of weight,volume,vertical and horizontal diameter in HN-001 and HN-004 were faster than those of HN-002,the mean weight were between 421.47 g to 539.07 g so they belong to large fruit . Fruit shape Index were 1.11, 1.64, the type were nearly circular and long circular, respectively; Fruit shape index of HN-002 was 0.9, small fruits and fruit nearly round.2). The flesh color of each inbred line melon were green (0 to 10 day) and turned Yellow-green ( 15 to 20 day).The color difference were turned at 25 to30 days.With the lightness of fruit decreasing gradually ,flesh brightness dimed. With Red-green index increasing and Yellow-blue index decreasing, flesh color become white gradually in HN-001. While Red-green index decreasing and Yellow-blue index increasing in HN-002,Flesh color become green gradually; At the same time Red-green index and Yellow-blue index increasing in HN-004, Flesh color become Orange-red gradually .3).During the development fruit firmness gradually decreased,and total soluble solid content increased. Total soluble solid of HN-002 is 9.84%, significantly higher than that of other two inbred lines. 2.Change of sugar contents and activities of sugar metabolizing enzymes in developing fruit of mesocarpThere was higher Ivr activities (AI, NI) , SS cleavage and lower SS synthesis sucrose,SPS activities in early developing fruit of three melon inbred lines, while the content of glucose ,fructose and total soluble sugar contants increased stablely ,almost no sucrose accumulated .In mid and latter stages of the HN-001 and HN-002 mesocarp development(15~40 d),there was higher SPS and SS synthesis sucrose activities and lower Ivr activities (AI, NI) ,the SS activities reduced quickly in the HN-002 and increased stablely in the HN-001. Sucrose content increased rapidly at the same time , fructose, glucose and total sugar did not changes. Sucrose accumulation and SPS activity were significantly positively correlated(HN-001,r=0.874*;HN-002,r=0.758),but SPS activity was relatively low in this period, the sucrose had been less accumulated in the whole fruit development , fructose, glucose and total soluble sugar contants were stabled in the HN-004,SS cleavage sucrose activity had not been changed, and had not significant relationship with sucrose accumulation.3. Sugar contents and activities of sugar metabolizing enzymes in the fruit of placenta:Sugar contents and activities of sugar metabolizing enzymes in placenta had the same trends with mesocarp in the fruit. In early developing fruit, Ivr activities (AI, NI) of placenta were lower than that of mesocarp. Sucrose accumulation in placenta were higher, while fructose and glucose contents were less than in the mesocarp. In mid and latter stages, the sucrose content of HN-001 and HN-002 was higher than fructose and glucose content from 35 d , but still lower than the total soluble sugar contents. While the sucrose content of HN-004 was significantly lower that that of fructose and glucose contents. Therefore, all three inbred lines were reducing sugar accumulation of melon fruit.4.The relationship of sugar gradient accumulation between mesocarp and placenta:The sucrose were accumulated in placental tissue and in the mesocarp at the same time but the sucrose in placental tissue were significantly higher than in the mesocarp of HN-001 and HN-002. The correlation coefficient of SPS activity and sucrose contents(r=0.932*)was higher than that of mesocarp(r=0.758)of HN-002. The sucrose in the placenta began to accumulate more 10 days than that of mesocarp, but also accumulate less and slowly of HN-004. The sugar accumulation propel from internal to external of the melon fruit.
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