Metabolomics Analysis Of The Responses Of Phragmites Australis At Different Ontogenetic Stages To The Change In Insect Feeding Pressure

Plant can take more flexible strategies to achieve the more reasonable energy allocation and trade-off between defense and growth/reproduction due to their defensive responses to insect herbivory.The composition and levels of plant metabolites play important roles in plant-insect interactions.How to explore the metabolomic responses of plant to insect herbivory by using the metabolomic approach so as to reveal the defensive strategies of plant and their impact factors has become an important direction of current research.In this thesis,based on gas chromatography mass spectrometry(GC/MS)based approach,the metabolomics analysis method of Phragmites australis(Cav.)Trin.ex Steud,an important plant in wetland,were developed,and the metabolomic profiling of P.australis under different feeding pressure treatments of Laelia coenosa(Hubner)and Dimorphopterus pallipes(Distant),two of the most important hebivore insects of P.australis,were analyzed.In addition,the changes in metabolomic responses of P.australis at different ontogenetic stages to the herbivory of these two herbivore insects were also analyzed.The study results were listed as follows:1.Effects of different drying methods on the metabolomics analysis of P.australis Based on gas chromatography mass spectrometry(GC/MS)approach,the effects of freeze drying,oven drying at 45 ? and silicone drying on the metabolomics analysis results of leaf,stem and root samples of P.australis were explored with ultra-low temperature preservation as a contrast method.The results showed that,although caused the significant increase in several metalolite content of leaf samples,freeze drying had no significant effects on the levels of metabolites in stem and root samples,and was the method with the least impact on metabolomic composition of different tissue samples.However oven drying at 45 ? and silicone drying had significant effects on the metabolomic composition of all tissue samples of P.australis.Therefore,freeze drying is the most suitable drying method for the sample preparation of metabolomic analysis of P.anstralis.2.The metabolomic responses of P.australis to the changes in feeding pressure of different insectsThe effects of different feeding pressure of L.coenosa and D.pallipes on the metabolome of leaves,stems and roots of P.australis were studied by feeding experiment.The results showed that the metabolomic responses of P.australis to the herbivory of two insects were tissue-specific.The metabolomic response of leaf tissue was more sensitive than responses of stem and root tissues.In addition,the metabolomic composition of P.australis tissues simultaneously fed by two insect species was different from those of tissues fed only by one of these two insect species.However,this treatment difference was only significant at high feeding pressure.The further analysis of metabolite content variation showed that feeding by two insect species had significant effects on various metabolites including sugars,amino acids,lipids and organic acids in P.australis tissues.The responses of some metabolites to insect herbivory were dependent on the plant tissues where they located,and the insect species including in the feeding treatment.The interaction effects of two insect species herbivory on the content level of some metabolites can be antagonistic and synergistic,and was associated with feeding pressure:significant under high but not low feeding pressure.This was consistent with the results of metabolomic response analysis.Under different feeding pressure,the change in the synthesis and allocation of metabolites in different tissues of P.australis may be an important explaination for these phenomena above.3.Different response strategies to insect herbivory of P.australis at different ontogenetic stagesThe metabolomic responses of leaves,stems and roots of P.australis to high and low feeding pressure of L,coenosa and D.pallipes were studied by feeding experiment.It was shown that the metabolomic responses of leaves and stems of P.australis to insect herbivory were significantly weaker at mature stage than at juvenile stage,while the responses of roots were slightly stronger.The seedling of P.australis at juvenile stage preferred to improve the sugars and amino acids content in leaf tissues whereas P.australis at mature stage preferred to improve the sugars acontent in stem and root tissues fter fed by two insect species.These results indicated that P.australis at different ontogenetic stages had different response strategies to insect feeding,and were consistent with the prediction of optimal-defense hypothesis.Results of this study also suggested that there were different and opposite trends in responses of metabolites of P.australis at different ontogenetic stages to the changes in insect feeding pressure.This result further confirmed that insect feeding had an important effect on the transport,allocation and synthesis of metabolites of different tissues of P.australis at different ontogenetic stages.4.Effects of herbivory induced response of P.australis on insect developmentIn this study,we investigated the effects of the metabolomic responses of P.australis induced by L.coenosa and D.pallipes herbivory on the development of larvae and nymphs of these two insect species.The results showed that feeding on P.australis previously attacked by L.coenosa and D.pallipes had different effects on the development of the larvae and nymphs of these two insects but the difference wss not significant.The responses of P.australis induced by L.coenosa herbivory had negative effect on the weight gain and the growth rate of its own larvae.However,the responses of P.australis induced by D.pallipes herbivory had a positively effect on the weight gain of its nymphs.Our results suggested that the effects of insect herbivory induced metabolomic responses of P.australis on the interactions between P.australis and its insect herbivores may be more complex than what our study revealed and should be further explored.In summary,the results of this thesis revealed the metabolomic responses of the P.australis at different ontogenetic stages to the herbivory of different insect species,and the changes in these responses when under different insect feeding pressures.These results provide an important reference for the future study of herbivory induced plant defense,and also will promote the use of plant metabolomics on the research of plant-insect interactions.