Effect of Calcium Nitrate on Sugar Content and Sugar-metabolic Enzyme Activities in Grafted Muskmelon Fruit
LI Tian-lai1，LI Ji-yao1，LIU Yi-fei1，2
1Key Laboratory of Liaoning Province for Protected Horticulture，Key Laboratory for Protected Horticulture，Ministry of Education，College of Horticulture，Shenyang Agricultural University，Shenyang 110866，Liaoning，China|2 Key Laboratory of Liaoning Provence for Resources and Environment，Key Laboratory for Soil and Environment in Northeast China，Ministry of Agriculture，College of Land and Environment Sciences，Shenyang Agricultural University，Shenyang 110866，Liaoning，China
Abstract：In order to solve the problem of sugar content decrease in grafted muskmelon（Cucumis melon L.）fruit，the self-rooted and grafted muskmelon were taken as test materials，the effects of different calcium nitrate concentrations on sugar-metabolic enzymes activities in grafted muskmelon fruit were studied．The result indicated that the effects of different nitrate calcium concentrations on sugar contents in the grafted muskmelon fruit were different．Compared with the control，the treatment of 0.5 % nitrate calcium concentration significantly increased the fructose，glucose，sucrose and galactose contents，while significantly decreased the raffinose and stachyose contents in the later part of fruit development（14-42 days after treatment）．Although the treatment of 0.2 % and 0.8 % nitrate calcium concentrations affect the soluble sugar content to some extent，the affecting degree is lower than the 0.5 % treatment．Three levels of calcium nitrate treatments significantly increased the total fruit sugar content 21 days after treatment，and 0.5 % calcium nitrate treatment also significantly increased the starch content．However，compared with the self-root control，0.5 % calcium nitrate treatment did not increase the contents of fructose，glucose，sucrose，starch and total sugar to the level of self-rooted muskmelon fruit．In view of fruit sugar metabolism and galactose metabolism enzymes，compared with the grafted control，each level of calcium nitrate treatment has significantly enhanced the acid invertase，alkaline α-galactosidase and sucrose phosphate synthase activities in the mid stage（14-28 days after treatment）of fruit development，yet sucrose synthase and neutral invertase activities had no change．Compared with self-rooted control，0.5 % calcium nitrate treatment could not increase the acid invertase activities to the level of self-root，but the sucrose phosphate synthase activities were improved obviously．The results indicated that different levels of calcium nitrate treatments can enhance starch，total sugar，glucose，fructose and sucrose content in grafted muskmelon fruit，and enhance acid invertase，alkaline α-galactos- idase and sucrose phosphate synthase activities．Among them，the effect of 0.5 % concentration calcium nitrate treatment is the best．These results suggested that increasing sucrose content in the mid or later part of fruit development may improve the quality of grafted muskmelon fruit.
