Epigenetic Variation Characteristics And Physiological And Ecological Responses Of DNA Of Invasive Plant Flaveria Bidentis Under Heavy Metal Cadmium And Saline-alkali Stress

In order to explore the tolerance of invasive plant Flaveria bidentis to abiotic stress,two typical habitats were selected in this study,which were contaminated by heavy metal cadmium?Cd?and complex saline-alkali stress.Three concentrations of cadmium(2,4 and 8 mg kg^-1)and 150 mmol L^-1 saline?p H 7.50,8.22,8.96 and 9.63?were simulated by pot experiment in net room.The plasticity of Flaveria bidentis under two stresses was studied by measuring its growth and physiological and ecological indices.The Methylation Sensitivity Amplification Polymorphism?MSAP?technique was used to analyze the variation characteristics of genomic DNA methylation in leaves of Flaveria bidentis under different treatments,and to further explore the characteristics of genomic DNA methylation in leaves of Flaveria bidentis.The correlation between phenotypic plasticity and epigenetic variation of Flaveria bidentis will provide an important theoretical basis for elucidating the ecological adaptability mechanism of it and for further understanding the invasiveness of plants.The main research contents and results are as follows:1.Flaveria bidentis has strong tolerance under low and medium concentration of Cd pollution,while plant regulation ability is weakened under high concentration of Cd pollution.It was found that when Cd concentration was less than 4 mg·kg^-1,the plant height,root growth and biomass of Flaveria bidentis did not change significantly,but when Cd concentration reached 8 mg·kg^-1,the growth and development of Flaveria bidentis decreased significantly compared with the control group.The activities of Superoxide dismutase?SOD?,Peroxidase?POD?and Catalase?CAT?increased first and then decreased with the increase of cadmium concentration,but they were higher than those of the control group,indicating that plant protective enzymes had limited energy-saving ability to regulate cadmium.The Cd content in different tissues of Flaveria bidentis showed that the increase of cadmium concentration inhibited the accumulation and transfer ability of it.The Cd content in Flaveria bidentis showed the rule of root > leaf > stem.With the increase of Cd concentration,the aboveground and root enrichment coefficients increased first and then decreased,reaching the maximum at Cd concentration of 4 mg kg^-1,and high Cd pollution reduced the transfer coefficient of Flaveria bidentis.Phenotypic plasticity studies showed that Flaveria bidentis accumulated nutrients mainly through maintaining root and leaf biomass,and adapted to heavy metal pollution habitats by regulating Cd accumulation in vivo.2.Flaveria bidentis was tolerant to low p H saline-alkali habitats.It was found that high p H inhibited plant height,root growth and biomass of Flaveria bidentis.Compound saline-alkali stress promoted photosynthesis of it at low p H.Net photosynthetic rate,stomatal conductance and transpiration rate were significantly inhibited when p H reached 9.53.The activity of protective enzymes showed that the active oxygen was scavenged by SOD and POD enzymes in the early stage of Flaveria bidentis,and regulated by CAT in the later stage of it.The osmotic regulators in leaves of Flaveria bidentis were determined.It was found that proline had protective effect on membrane system under compound saline-alkali stress with p H between 7.50 and 8.96.The soluble sugar in leaves was sensitive to saline-alkali environment.Under saline-alkali stress,the root biomass,stomatal conductance,electrolyte leakage rate and phenotypic plasticity index of free proline of Flaveria bidentis were higher?PPI > 0.5?.This indicated that Flaveria bidentis could absorb and accumulate nutrients mainly by changing root biomass and controlling stomatal opening,and balance cell osmotic pressure through electrolyte exosmosis rate and free proline content.3.Under Cd stress,a total of 726 bands were amplified by 15 pairs of primers.The fully methylation and total methylation levels of leaves of Flaveria bidentis increased,and the main variation pattern of methylation was re-methylation.Phenotypic plasticity was negatively correlated with phenotypic plasticity of Flaveria bidentis growth index and aboveground tolerance index,and positively correlated with antioxidant enzyme activity,Cd content in tissues,accumulation and transfer coefficient.Under combined saline-alkali stress,585 bands were amplified from 15 pairs of primers,and the level of semi-methylation in leaves increased,mainly in the mode of demethylation variation.The increase of DNA total methylation level induced phenotypic plasticity of growth and photosynthetic indexes of Flaveria bidentis to promote the accumulation of organic substances.The increase of semi-methylation level induced phenotypic plasticity of soluble protein and electrolyte exosmosis.The increase of plasticity regulates osmotic stress and controls cell osmotic pressure balance.