Effects Of Grafting On Nitrogen Metabolism In Melon Seedlings

The massive application of nitrogen fertilizer not only increases the cost of agriculture,hinders the rapid development of agriculture,but also destroys the ecological environment.In recent years,the growing area of melon has been expanding,and the degree of intensive cultivation and production has gradually increased,resulting in a series of soil problems.However,grafting is widely used as a cultivation technique and alleviates the relationship between fertilization and yield to a certain extent.The experiment was conducted in type Liaoshen?greenhouse,muskmelon seedlings by grafting for treatment,with own root muskmelon seedling as control.The contents of the experiment were divided into three main parts.First,the biomass of scions,nitrogen content,leaf and total nitrogen content,nitrogen accumulation,distribution of nitrogen,key enzyme activity of nitrogen metabolism,key gene expression,and the effect of grafting on nitrogen assimilation of melon seedlings were determined.Secondly,the ¹⁵N isotope tracer test was used to grow to 7th leaves melon.During the period,the isotope tracer markers were used to select different processing times and to sample the melon seedlings from the bottom to the bottom,to determine the content of¹⁵N in different nodes and to determine the transport rate of nitrogen in the melon plants.Finally,the carbon-nitrogen ratio of the plants,the relative expression of nitrogen transport protein and sugar transporter gene,and the upstream of nitrogen metabolism and transporter related genes were measured.The difference of HY5 transcription factor gene expression between different time and space was analyzed,and then the effects of grafting on C/N ratio and CmHY5 gene expression in melon seedlings was claried.The results are as follows:1.Effects of grafting on nitrogen metabolism of melon seedlings:with the growth and development of muskmelon seedlings,the dry weight and fresh weight of the grafted and control melon seedlings showed a rising trend,and the difference was significantly between the seedlings age and the relative water content in the upper part of the melon seedlings.The content of ammonium nitrogen and nitrate nitrogen in the leaves of the grafted melon was significantly higher than that of the control.and the increase of nitrate and ammonium nitrogen in the 5th leaf stage was the most obvious,It was 1.4 times and 1.45 times than that of the control,respectively.and the nitrogen content in the upper part of the grafted melon was significantly higher than the control,and the nitrogen accumulation was significantly increased.The nitrogen content in the leaves also increased significantly.The soluble protein content and non protein content in the grafted leaves were significantly higher than those of the control.The activities of the NR,GS,GOGAT,GOT and GPT enzymes in the leaves of the grafted melon were significantly higher than those of the control.The grafting increased the activities of the key enzymes of nitrogen metabolism,and the relative expression of the CmNR and CmGS genes in the leaves of the melon was grafted in the relative expression of the key enzyme gene of nitrogen metabolism.Significantly higher than that of the control,grafting on transcriptional level affected the expression of key enzymes related to nitrogen metabolism.2.Changes of ¹⁵N transfer and distribution in Muskmelon Seedlings:¹⁵N was detected in the roots of the melon plants after 0.5 h marked by ¹⁵N isotope.After the labeling of 4 h,¹⁵N had been transported to all parts of the melon plants.After labeled 4 h,¹⁵N in melon plants mainly distributed in roots and young leaves,but less in melon leaves.In the detection of ¹⁵N abundance in rhizosphere soil,the abundance of grafting and control decreased,and the abundance of ¹⁵N in the rhizosphere soil of the late grafted melon was lower than that of the control.However,grafting did not affect the rate of nitrogen transport and the distribution in different organs.3.Effects of grafting on carbon-nitrogen ratio of melon seedlings:The total carbon content and total nitrogen contents of the leaves were significantly higher than those of the control.With the growth of melon seedlings,the ratio of C to N between leaves and shoots of grafted melon seedlings has a decreasing trend compared with CK.Grafting affected the C/N ratio of leaves and plants of the melon seedlings,and reduced the C/N ratio.The expression of sugar transporter and nitrogen transporter related genes showed that the relative expression of nitric acid transporter gene?CmNRT2.4,CmNRT2.5?and ammonium salt transporter gene?CmAMT2,CmAMT3?in the grafted melon seedlings was up,the expression of CmSweet1gene of sugar transporter gene was up regulated,and the expression of CmSweet4 and CmSweet12 gene was down regulated.Grafting affects the expression of transporters in melon leaves at the transcriptional level.4.Role of transcription factor HY5 in nitrogen metabolism of melon:HY5 is the regulator of the upstream of the transporter protein.The detection of CmHY5 gene expression in melon leaves under different illumination conditions shows that the grafting can induce the expression of CmHY5 gene expression in the leaves of melon significantly up under natural illumination conditions.Analysis of the temporal and spatial differential expression of CmHY5 gene showed that CmHY5 gene expression increased gradually during seedling growth stage.Grafting was higher than control.In the analysis of gene expression in three organs of root,stem and leaf,it was found that the relative expression of genes in the grafted muskmelon increased significantly,and the expression of the leaves was up to the highest.In summary,the nitrogen content,the key enzyme activity,the relative expression of the enzyme active gene and the relative expression of the transporter genes in the grafted muskmelon were significantly higher than those of the self rooted melon seedlings,and the biomass of the aboveground increased significantly,and the growth trend also increased.The relative expression of CmHY5 gene in grafted melon seedlings was increased.Based on the regulation of HY5 transcriptional factors on nitrogen operation and assimilation,the effect of grafting on the relative expression of CmHY5 gene was a possible way to enhance the nitrogen metabolism capacity.