Researches On Physiological Mechanism Of Exogenous H₂O₂ To Improve Salt Tolerance In Cucumis Sativus L.

Secondary salinization of soil was process of soil salinzation,which resulted by secondary irrigation.And it constantly caused by secondary salinization of soil.The cucumber（Cucumis sativus L.）is one of the primary vegetables cultivated in the field and the establishments.The yield of cucumber were obviously reduced by secondary salinization of soil.At present,it is a hotspot on the relation between the plant resistance and H₂O₂,as signaling molecules.However,experimental study on the relation between the salt tolerance of cucumber and H₂O₂ were few reported.Seedling of six cultivars of cucumber were used as experimental materials to study effects of different concentration of Na Cl treatments on growing state,leaf fresh weight,leaf dry weight,leaf area,physiological indexes of relative electric conductivity（REC）,contents of malondialdehyde（REC）and the hisochemical allocation of the superoxide anion（O₂˙ˉ）.By the method of subordinate function,comprehensive evaluation on the salt resistance of six cultivars of cucumber was made.Then the salt tolerant cucumber and the salt dependent cucumber were screened.To investigate the effect of H₂O₂ on the physiological mechanism to cucumber which under salt stress,the salt dependent cucumber Chunxiaqiuwang was selected as experimental materials.And it was processed by exogenous H₂O₂.The growing state,the cell membrane permeability（REC and MDA）,the accumulation of active oxygen（H₂O₂ and O₂˙ˉ）,the changes of anti-oxidative system（ascorbic acid,reduced gluathione,superoxide dismutase,catalase,peroxidase and gluathione reductase）,and the differentially expressed proteins was analyzed.The main findings were as follows:（1）Results showed that with the increased of salt concentration of Na Cl,leaf fresh weight,leaf dry weight and leaf area decreased significantly.Both of the relative electric conductivity and the contents of malondialdehyde showed a rising trend.Cell membrance damage of leaf gradually increased.The results showed that the O₂˙ˉdyeing area increased in cucumber leaf by hischemical allocation.The studies confirmed that the six cultivars of cucumber salt resistance order is“Jinyansihao”>“Xinjinyanqihao”>“Xinjinchunsihao”>“Xinjinyouyihao”>“Tangshanqiugua”>“Chunxiaqiuwang”by the method of subordinate function.（2）Compared with the control group,the plant height,leaf area,fresh weight and dry weight decreased significantly under 200m M salt stress.Both of REC and the contents of MDA showed a rising trend.The result showed that the growth of cucumber was inhibit by salt stress.And cell membrance damage gradually increased.It showed that H₂O₂ had significant rescue adverse effects on Na Cl stress-induced inhibition of growth and damage on cell memebrane.（3）Compared with the control group,the contents of O₂˙ˉin the leaf remained when it increased in the root under salt stress.Then the contents of O₂˙ˉin the root by exogenous H₂O₂.The contents of O₂˙ˉin the leaf and root increased while it decreased by exogenous H₂O₂.The contents of gluathione（GSH）and ascorbic acid（As A）decreased,but it showed the opposite tendency by exogenous H₂O₂ in the leaf and root.The activity of peroxidase（POD）was improved with process in the leaf and root.The activity of gluathione reductase（GR）in the leaf was improved,while it showed an opposite character in the root.It showed no apparent changes on superoxide dismutase（SOD）and catalase（CAT）.（4）The SDS-PAGE result analysis that,compared with the control group,three protein bands were up-regulated and four were down-regulated in the leaf under salt stress.Meanwhile,four protein bands were up-regulated and four protein bands were down-regulated in the roots.According to the change of the differentially expressed proteins,four protein bands were analysed by MALDI-TOF-MS,which get changed observably.The results showed that probable methyltransferase PMT5 may be related to improving salt tolerance by exogenous H₂O₂.The above results indicate that in order to improving salt stress,H₂O₂may alleviate the inhibition of growth and damage on cell membrane caused by salt stress in cucumber via acceleration of antioxidant,activation of antioxidase and expression of protein.