Effects Of Intercropping With Wheat On Sugar And Nitrogen Metabolism And Expression Of Differential Proteins In Cucumber Leaves

Cucumber（Cucumis sativus L.）occupies important economic status in the agricultural production of our country.Cucumber leaves will premature under unfavorable conditions,which leads to the shortened cucumber fruit bearing stage and the decrease of yield.the premature of leaves caused by continuous monocropping is an important factor restricting the long season cultivation of cucumbers,which not only increased plant diseases and insect pests,reduced yield and quality of vegetables,but also causes premature aging of plants.Therefore,continuous monocropping obstacle has become an important problem to be solved in the vegetable industry in china.Sugar and nitrogen metabolism are important metabolic activities of crops,which are closely related to the senescence of crops.The preliminary research results of our research group showed that intercropping with wheat and cucumber can effectively alleviate continuous monocropping obstacles and delay cucumber leaf senescence.However,there is no report to date about the change of sugar and nitrogen metabolism and leaf differential proteins during the senescence of cucumber leaf under the cultivation mode of intercropping with wheat.In this experiment,a greenhouse experiment was conducted in the continuous cropping soil environment,which to study the effect of intercropping with wheat on physiological indicators of sugar and nitrogen metabolism in the process of cucumber leaf senescence,and the iTRAQ（isobaric tags for relative and absolute quantitation）technology has been adopted in order to analyse the quantitative differential proteins in cucumber leaves,which to investigate the differences of proteins expression level in cucumber leaves in treatment of cucumber monoculture and intercropping with wheat.These differential proteins were further analyzed by bioinformticstools,which aims to explore the physiological changes and the molecular mechanism of intercropping with wheat delaying senescence of cucumber leaves,in order to clearing the effect on intercropping with wheat during the senescence of cucumber leaves,and building the foundation for further study on the senescence of cucumber.Main conclusions are as following:1.Cucumber plant height,stem diameter and fresh and dry weight of shoot/root part of each sampling period of the trement of intercropping with wheat is higher than that of cucumber monoculture.And during the whole growth cycle,the yield of cucumber treated with intercropping with wheat was significantly higher than that of cucumber monoculture.2.In a certain extent,the content of soluble sugar,reducing sugar,glucose and sucrose in cucumber leaves were significantly lower in CWI（cucumber/wheat intercropping）system than that in CM（cucumber monoculture）system,and the activity sucrose synthase（SS）,sucrose phosphate synthase（SPS）,neutral invertase（NI）and acid invertase（AI）were higher than in CWI（cucumber/wheat intercropping）system than that in CM（cucumber monoculture）system;qRT-PCR analysis showed that compared with CM（cucumber monoculture）system,the expression of CsSS（sucrose synthase）,CsSPS（sucrose phosphate synthase）,CsSUT4（sucrose transporter）in CWI（cucumber/wheat intercropping）system were up-regulated.3.Compared with CM（cucumber monoculture）system,the content of soluble protein,free amino acid,nitrate nitrogen and proline in CWI（cucumber/wheat intercropping）system were higher in cucumber leaves;the activity of NR（nitrate reductase）,GS（glutamine synthetase）,GDH（glutamate dehydrogenase）and GOGAT（glutamate synthase）in CWI（cucumber/wheat intercropping）system were higher than that in CM（cucumber monoculture）system of cucumber leaves;qRT-PCR analysis revealed that compared with cucumber monoculture,the expression of N1,N2 and N3,which belong to NRT（Nitrate Transporter Protein）family and A1,which belong to AMT（Ammonium Transporter Protein）family and GS1（cytosolic glutamine synthase gene）were up-regulated in intercropped cucumber.4.The iTRAQ technique was used to analyze the quantitative differential proteins analysis of the 4^th cucumber leaf age was 40 d.A total of 93 differential proteins were found,of which 2 were up-regulated and 91 were down-regulated.These differential proteins are mainly related to the molecular functions of binding and catalytic activity.The biological processes involved are mainly cellular processes and metabolic processes;GO enrichment analysis shows that compared with cucumber monocropping,the differential proteins are mainly enriched in biological regulator,molecular function regulator and transporter activity.The KEGG Pathway enrichment analysis demonstrated that the treatment of intercropping with wheat promoted significant changes in the glycosphingolipid biosynthesis and other glycan degradation pathways in cucumber leaves.In summary,the treatment of intercropping with wheat promotes the growth of cucumber plants,enhances the sugar and nitrogen metabolism activities of cucumber leaves,induces the expression of genes related to sugar and nitrogen metabolism,and triggers significant metabolic changes in these pathways of sphintoglycolipid biosynthesis and polysaccharide degradation.To a certain extent,the cultivation mode of intercopping with wheat has an effect on the metabolism of sugar and nitrogen in cucumber leaves,which is beneficial to delaying the senescence of cucumber leaves.