| Drunken horse grass(Achnatherum inebrians)-(Epichlo? gansuensis)symbionts as the research matierial,induced by bird-cherry aphid(Rhopalosiphum padi)and spraying salicylic acid(SA)and exogenous methyl jasmonate(MJ),the defense capability of the plant physiology and nutrition related indicators and hormone signaling pathways related expression of transcription factors,hormone signaling pathways and the relationships between the endophytic fungi were determined.In addition,the response of aphid to endophyte infection and hormone-induced resistance was investigated by observing the pea aphid(Acyrthosiphon pisum)growing on the seedlings of drunken horse grass which had been infected by endophyte and treated by SA.The main results are as follows:1.By SA signaling pathway of plants induced by aphid feeding,it was found that endophyte improved the growth compensation ability of(Endophyte-infected,E+)plants under biological stress,and inhibited the endogenous SA level.The shoot biomass,underground biomass,plant height and PPO activity of E+ plants were significantly higher than those of(Endophyte-free,E-)E-plants(P<0.05).The SA level in E-plants was significantly higher than that in E+ plants,while the JA level in E+ plants was not significantly affected by endophytic fungi and insect grafting(P>0.05).The expression level of WRKY54 transcription factor in E+ plants was significantly higher than that in E-plants(P<0.05),but the expression level of WRKY57 transcription factor in E+ plants was significantly lower than that in Eplants(P<0.05).2.By SA signaling pathway of plants induced by exogenous SA spraying,it was found that the endophyte increased the JA level in E+ plants.Under the treatment of exogenous SA,both endophyte and exogenous SA significantly affected the dynamic changes of JA level in E+ plants(P<0.05),and the level of JA in E+ plants was significantly higher than that in E-plants(P<0.05).The content of SA in E-plants was higher than that in E+ plants,but not significantly(P<0.05).Above-ground biomass,underground biomass,plant height and chlorophyll content of E-plants were all lower than those of E+ plants.The PAL activity in E-was higher than that in E+plants.Under low concentrations of exogenous SA(5 m M,10 m M),the expression of WRKY54 in E+ plants were significantly higher than that in E-plants(P<0.05),and the expression of WRKY57 in E+ plants was significantly lower than that in E+ plants(P<0.05).3.By JA signaling pathway of plants induced by exogenous MJ spraying,it was found that exogenous MJ could induce changes in nutrients both in E+ and E-plant,produce related defense enzymes,and have a gain effect on insect resistance.Under MJ treatment,the soluble sugar content and chlorophyll content in E+ seedlings were significantly(P<0.05)lower than that in the control but higher than that in Eseedlings,the total phenol content and TI activity were significantly(P<0.05)higher than that in the control and higher than that in E-seedlings.The PPO and PAL activities of E+ plants were significantly higher than those of the control and E+plants(P<0.05).4.By observing the poisoning symptoms of aphid on the endophytic fungi infected and SA treated E+ plants,it was found that the aphids growing on CK Eplant showed normal activity,with normally-shaped legs and antennae.However,pea aphids on the CK E+ plants showed obvious poisoning symptoms,where the aphids did not show normal "standing" posture,and the femur-tibia joints gradually extended,raising the unilateral trembling middle leg,after the trembling of the antennae and legs,the pea aphids became deeply paralyzed and dead.Under SA treatment,the aphids on SA E-plants showed no obvious poisoning symptoms compared with E+,but showed leg lifting,mild tremor and other symptoms.Symptoms of aphid poisoning on SA E+ plants are similar to aphids of CK E+ plants,the femur-tibia joints gradually extended,a slight trembling of the antennae and legs was evident,and legs gradually huddled around to the abdomen.5.By observing the changes of the nutrients in aphids subcultured on the endophytic fungi infected and SA treated seedlings,it was found that nutrient content in aphids on E+ plants for three successive generations was insensitive to exogenous SA treatment,while the nutrients of aphids on E-plant was sensitive to SA treatments.We suggest that the grass-endophyte symbiont produces alkaloids as its main insect-resistance strategy,and the toxicity of alkaloids on pea aphid is stronger than the defense effect of the plant salicylic acid signaling pathway. |
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