Physiological Response Of Pea And Rhizobium Symbiosis To Salt Stress

This study was aim at illuminating the physiological response of peas inoculated rhizobia to salt stress.In this paper,two varieties of pea（Pisum sativum）seeds and three strains of rhizobium were used as experimental materials to inoculate peas with rhizobium by soaking the seeds in bacterial broth,and pot experiment was conducted to study the physiological response of pea and rhizobium symbiosis to salt stress.In experiment 1,3 NaCl stress levels were set:no salt stress（applied deionized water）,mild salt stress（applied 35 mmol·L^-11 NaCl solution）and high salt stress（applied 105 mmol·L^-11 NaCl solution）.A total of 12 treatments were used for control group and 3 strains of rhizobium.In experiment 2,three CaCl₂concentrations were set:no addition,low concentration（applied with 5 mmol·L^-11 CaCl₂solution）and high concentration（applied 15 mmol·L^-11 CaCl₂ solution）,control group and three different strains of rhizobium were used,and 35 mmol·L^-1NaCl solution was used for stress treatment.1.Inoculating rhizobia could enhance the salt tolerance of peas,and its effect was related to the strains of rhizobia and the varieties of peas.In this experiment,Dingwan 8 had strong inoculation effect on ACCC15657 and ACCC15735,and had little effect on Ca66.Longwan 6had the best inoculation effect on ACCC15735,and also had good effect on Ca66.Rhizobium inoculation had no significant effect on plant height,but 15735 had significant effect on fresh weight of Longwan 6.The salt tolerance of Dingwan 8 inoculated rhizobia was higher than the control group.Under mild stress,in 15735 inoculation treatment,the activity of SOD increased by 116.59%,44.03%and 28.16%respectively at three growth stages,the MDA content decreased by 48.33%and 57.55%at flowering and fruiting stages.Proline content increased by 21.71%,22.63%,18.55%and soluble sugar content by 192.43%,132.93%,69.18%respectively at three growth stages.Similar results were obtained under severe stress.The change of POD activity was contrary to that of SOD.When SOD activity was higher,POD activity was weaker in most results.Longwan 6 inoculated rhizobia had similar effect as Dingwan 8,but the effects were weaker than that found in Dingwan 8.2.The salt tolerance of pea could be enhanced by applying appropriate amount of exogenous CaCl₂.The effect of 15 mmol·L^-11 CaCl₂solution was stronger than that of 5mmol·L^-1CaCl₂solution.In CK treatment without inoculation,MDA content of Dingwan8 at seedling stage reduced by 23.67%and 39.56%respectively at low and high CaCl₂ concentration,meanwhile the proline content increased by 16.99%and 48.05%,the soluble sugar content in the increased by 19.72%and 61.06%,SOD activity increased by 16.42%and56.15%.Other groups showed similar changes.It indicated that exogenous CaCl₂ could enhance salt tolerance of pea.3.Both the proper rhizobium inoculation and the application of exogenous CaCl₂ could enhance the salt tolerance of pea.When CaCl₂ solution was applied to peas inoculated with rhizobia,if the rhizobium and the peas had good macthing,the effect of CaCl₂ solution on the physiological indexes of peas was weak;If the matching between rhizobium and peas was poor,the effect of CaCl₂ solution on the physiological indexes of peas was strong.In Dingwan8 inoculated with ACCC15657,its SOD activity was respectively increased by 27.95%and51.55%after 5 mmol?L^-11 CaCl₂ and 15 mmol?L^-11 CaCl₂ were applied.The numbers in Dingwan 8 inoculated with ACCC15735 were 9.01%and 12.63%,which was lower than Dingwan 8 inoculated with ACCC15657.In non-CaCl₂ treatment under the same salt stress,SOD activity of Dingwan 8 inoculated with ACCC15657 increased by 18.76%at fruiting stage;SOD activity of Dingwan 8 inoculated with ACCC15735 incrased by 28.15%,which was higher than Dingwan 8 inoculated with ACCC15657.The above results showed that pea inoculated with appropriate rhizobia and applie appropriate amount of CaCl₂ can enhance its salt tolerance.The results of this study provide a basis for further study on the stress physiology of rhizobium pea symbiosis.