Cross Resistance In Ammopiptanthus Nanus Response To Salt Stress And Herbivore Feeding

Plants are often exposed to a wide range of abiotic and biotic stresses including salt stress and herbivore insects(Mittler,2006;Atkinson and Urwin,2012;Mantri et al.,2014).Due to their sessile speciality,plants cannot escape environmental cues as animals.Plants have evolved stress-defence and stress-tolerance mechanisms to cope with biotic and abiotic stress.Thus,it is significant to investigate the cross adaptability in plants response to different stress and will help to reveal the resistance signal network and develop breeding engineering.Ammopiptanthus nanus,an endemic evergreen broad-leaf shrub belonging to the genus legume,grows in the Xinjiang region of China and the mid-Asian deserts.As a relic plant from Tertiary subtropical evergreen broad-leaf shrub,A.nanus plays an important role in maintaining ecosystem balance and is thus listed as a Class II national protected species in China.Although some attention has been paid to the study on stress resistance of A.nanus,there are few reports on its cross resistance.Therefore,A.nanus and Orgyia ericae were used to study the cross resistance mechanism of A.nanus in response to insect feeding and salt stress.And the main research results are listed as follows:(1)Jasmonic acid(JA)content was elevated by herbivore pretreatment in A.nanus leaves and roots under salt stress.JA could be recognized by its receptor COI1,thus activated JA signaling pathway and elevated PM H⁺-ATPase activity,causing a large amount of transmembrane H⁺efflux.High level of H⁺efflux contributed to establishing proton electrochemical potential gradient,which not only provided proton driving force for the Na⁺/H⁺antiporter to expel excess Na⁺into medium,but also reduced K⁺leakage via DA-KORCs or DA-NSCCs by weaking V_m depolarization induced by NaCl.At the same time,the value of p H in cytoplasm was elevated due to H⁺efflux,which might trigger NADPH oxidase activity and H₂O₂generation.H₂O₂accumulation would contribute to elevation fo intracellular Ca²⁺concentration([Ca²⁺]_cyt).In this study,it was found that herbivore feeding decreased Ca²⁺efflux elicated by NaCl through repressed Ca²⁺-ATPase activity,triggered Ca²⁺influx via voltage-gated Ca²⁺channels and promoted the release of Ca²⁺from intracellular calcium stores,resulting in[Ca²⁺]_cyt elevation.On one hand,the elevated[Ca²⁺]_cyt might activate the SOS pathway and promote the activity of the Na⁺/H⁺antiporter.On the other hand,[Ca²⁺]_cyt might repress K⁺efflux induced by NaCl,thus help maintaining of K⁺/Na⁺ratio.Taken together,herbivore feeding reprogrammed plasma membrane ion channels or transporters activity in root cells of A.nanus through inducing JA accumulation and triggering JA signaling pathway.JA could promoted PM H⁺-ATPase activity,H₂O₂generation and[Ca²⁺]_cyt elevation,thus causing changes in transmembrane K⁺,Na⁺,Ca²⁺and H⁺flux in A.nanus exposed to salt stress.K⁺leakage and Na⁺accumulation in root cells were then limited at a low level,which finally maintained a higher K⁺/Na⁺ratio and improved A.nanus tolerance to salt stress.(2)In A.nanus mesophyll cells,salt-pretreatment enhanced Ca²⁺influx and[Ca²⁺]_cyt level triggered by oral secretions(OS)from O.ericae larvae though JA pathway.At the same time,salt stress also enhanced OS-induced H⁺efflux,which might be mediated by H⁺-ATPase or unknown OS-derived H⁺channels.These evidence indicated that salt stress enhanced ion early signaling in A.nanus mesophyll cells response to OS.(3)Salt stress promoted JA accumulation though linolenic acid accumulation and upregulation of LOX gene family(especially in 13-LOX subfamily).Then JA signaling pathwy was involved in enhancing A.nanus defense against O.ericae larvae,resulting in larvae growth inhibition.(4)K⁺loss caused by NaCl stress might be one of important reasons for A.nanus resistance to O.ericae larvae growth.A large amount of Na⁺entered into cells due to NaCl stress led to plasma membrane depolarization,resulting in K⁺leakage through DA-KORC and K⁺content decrease.Furthermore,that elicited Ca²⁺influx and[Ca²⁺]_cyt elevation,which might promoted PLD?activity and linolenic acid generation.JA accumution and JA pathway activation enhanced A.nanus defense against O.ericae larvae.In this study,the interaction mechanism in A.nanus response to herbivore feeding and salt stress was revealed.An early signal network of insect-plant-salt stress interaction was established,which will provide theoretical guidance for elucidating plant cross adaptability,development of biological pesticides and engineering breeding.