AMF Regulates Endogenous Hormone Responses And Systemic Drought Resistance Of Medicago Truncatula

Drought is one of the important factors restricting agricultural production.According to many studies,arbuscular mycorrhiza fungi(AMF)symbiosis can effectively improve the drought resistance of plants.Jasmonic acid(JA)and salicylic acid(SA)are phytohormones which play important role in biotic and abiotic stress responses,however,it is not confirmed that whether could participate in AMF symbiosis to improve plant drought resistance.Therefore,the model legume plant Medicago truncatula was used in the split-root system with two compartmens applied the treatment such as drought,inoculation of AMF,Rhizobium or dual inoculation.The objectives of this study were to investigate the change of on root dry weight,N and P nutrients,osmotic regulation ability,osmotic adjustment ability,antioxidase system,phytohormones including JA,SA,H2 JA and Jasmonoyl-L-isoleucine(JA-ILE)and their expression analysis of regulatory genes PAL and BIK1 of these indicators on root,and how to response to local AMF and drought signals,emphatically clarity whether dual inoculation have synergistic benefits and their mechanism in response to local drought,to explain the defense response mechanism of JA and SA and their complexes at local and systemic levels on roots of Medicago truncatula regulated by AMF and drought,verify the molecular biological evidence that AMF enhances systemic drought resistance by affecting JA and SA of key regulatory genes PAL and BIK1 under drought.The major conclusions are as follows:(1)The AMF was inoculation with well-watered significantly improved root dry weight and the absorption of P content nutrients,but had no significant effect on the content of N.Plants respond to local inoculation signal and realize the increase of the P content of the non-inoculated side.Local drought signal reduced the positive effect of AMF inoculation on root P absorption and meawhile decrease the root P content in another compartment.(2)The local inoculation of AMF increased the root system proline content of medicago truncatula and the activity of POD,CAT and APX,without the obvious influence on MDA content under well-watered condition.Because the inoculating signal activated system response mechanism,the proline content of the root on the non-inoculated side were increased and its antioxidant enzyme activity and ROS scavenging was enhanced,the lipid damage of plasma membrane were reduced.Local drought treatment lead to the massive accumulation of root system proline and the decrease of SOD,POD,CAT and APX activities under AMF symbiosis.(3)Local inoculation of AMF caused up-regulation of PAL and BIK1 expression on the uninoculated root,thus increased the content JA and JA-ILE.Local drought increased the expression of PAL and BIK1 on the AMF symbiosis,while the expression of two genes on the non-mycorrhizal compartment had no significant effect.After system responded to the local drought pathway,the content of two hormones on the non-mycorrhizal compartment under drought were decreased.(4)According to the treatment of dual inoculation,compared with Rhizobium symbiosis,the local inoculation of AMF was more significant in improving root P content,while the local inoculation of Rhizobium was more advantageous in increasing root dry weight and N content.There were no significant synergistic effect of local dual inoculation on the dry weight,N and P content.In mycorrhizal compartment,under well-watered treatment,inoculation of AMF could accumulate more proline than that under dual inoculation and Rhizobium symbiosis,while under drought,the proline content of Rhizobium was higher.Local dual inoculation treatment showed a significant synergistic effect on enhancing activities of SOD,CAT and APX,after regulated by local inoculation at the system level,showed synergistic effect in the non-mycorrhizal compartment.The results showed that plants could respond to local daul inoculation signal,realized systematic regulation and improved the activity of antioxidant enzymes in the whole root system.Under drought,local daul inoculation showed a significant synergistic effect on the promotion of PAL and BIK1,and caused regulation at the systemic levels.The JA content of daul inoculation was similar to that of single inoculation with AMF,and significantly higher than Rhizobium.These results preliminarily confirmed that local inoculation of AMF could effectively activate the hormone response mechanism which were centered by JA and JA-ILE and improve the drought resistance of host plant both at the local and systemic levels.