Regulation Of Healing Environment And Watermelon Scion On Root Growth And Sugar Metabolism Of Grafted Seedlings

The plant root system not only provides structural support for the overground,but also can absorb water and nutrients from the soil,and transport water,nutrients and hormones to other tissues or organs through the vascular tissue for its growth,development and reproduction.In this study,the watermelon"Zaojia 8424"was used as the scion,and the pumpkin"Weizhen No.1"was used as the rootstock,and two grafting combinations including watermelon/pumpkin（scion/rootstock,W/P）and pumpkin/pumpkin（P/P）were set up,using the one-cotyledon splice grafting method.The pumpkin seedlings without grafting（P,P₀）were used as control.The changes in root growth and vigor of watermelon/pumpkin grafted seedlings during graft healing and the effects of watermelon scion on the growth and vigor of grafted seedlings were studied,and the root sugar content,enzyme activity and the expression levels of related genes are compared.The main results were as follows:1.After grafting,there was no significant difference in the time and rate of phloem connection between W/P and P/P grafted seedlings,and they are gradually connected within 3 to 5 days after grafting;the xylem connection time of P/P grafted seedlings was slightly earlier than that of W/P grafted seedlings.The change trend of sugar content in W/P and P/P binding sites was consistent with that of grafting healing.After cutting,the content of total sugar,soluble sugar,reducing sugar and starch in the union top（the scion part）of the grafted seedlings gradually increased,and reached the highest level 3days after grafting,and then gradually decreased;while the content of total sugar,soluble sugar,reducing sugar and starch in the union down（the rootstock part）gradually consumed,its content was 2after grafting,and then gradually recovered;as the graft healed,the sugar content above and below the healing site gradually became consistent.The change trend of sugar content in the joints of grafted seedlings of W/P and P/P was consistent with that of phloem and xylem,and there was no significant difference between them.2.The sugar content of the root system of watermelon/pumpkin grafted seedlings during the graft healing period was significantly reduced,and the root growth and vitality were significantly inhibited.The weak light and high humidity during the graft healing period caused the seedling roots to grow slowly.Compared with the P₀ pumpkin seedlings cultivated in the greenhouse the root freshness,dry mass,root volume and root vigor of grafted seedlings W/P,P/P and pumpkin seedlings P were significantly decreased,and the total sugar,soluble sugar,reducing sugar and starch content in the seedling root it is also significantly lower than before grafting.The activities of SPS and SuSy in the roots of the seedlings increased first and then decreased after grafting,and reached the highest value 3days after grafting,and then gradually decreased with the improvement of healing environment;the activities of HXK and AGP were consistent with the changes of soluble sugar and starch content;CWIN activity was maintained during healing period.There was no significant difference in the detection of root growth indexes,sugar content and enzyme activity between grafted seedlings W/P and P/P.3.After the healing period,the effects of watermelon scion on root growth and sugar metabolism of grafted seedlings were further measured.The results showed that:（1）In W/P,the watermelon scion caused the root growth index（fresh quality,dry mass,and root volume）and root vigor of the grafted seedlings to be significantly lower than those of the P/P and P seedlings.（2）The contents of total sugar,soluble sugar,reducing sugar,starch,as well as sucrose,glucose and fructose in the roots of were lowest in the W/P grafted seedlings,but highest in P treatment.（3）Compared to the P/P and P treatments,watermelon scion caused lower activity of cell wall invertase（CWIN）and hexokinase（HXK）in the roots of W/P grafted seedlings,and accordingly,the expression levels of CWIN and HXK were significantly reduced.The results indicated that watermelon scion could repress the sugar accumulation in the roots of grafted seedlings and inhibit the enzymatic activity of CWIN and HXK,and thus suppress the root growth and vigor of grafted seedlings.