| Under the background of global climate change,soil salinization has become one of the most serious environmental problems.Soil salinization will change the physical and chemical properties of soil,affect the germination,growth and reproduction of plant seeds,and lead to the decline of plant biomass.Global crop yield reduces by more than 20%every year due to soil salinization.Saline alkali land is widely distributed in China,and nearly 7%of agricultural land is affected by salinization,so the ecological technology that repairs the soil salinization is urgently needed.Elaeagnus angustifolia L.is a perennial deciduous tree or small tree of Elaeagnus family.It has strong living abilities,the characteristics of tolerance to drought,salt,barren,wind and sand,and great economic values in food,medicine,paper making,forage,furniture,etc.,so it has been listed as the pioneer tree species for afforestation,soil improvement and ecological improvement in desert sand land and saline alkali land in China.Arbuscular Mycorrhizal Fungi(AMF)can establish arbuscular mycorrhiza(AM)symbiont with 80%of terrestrial plants.In terms of nutrient absorption,transport and utilization,AM is more efficient than individual plant roots.At present,the understanding of the mechanism of AM’s improving the salt tolerance of host plants is still in the stage of continuous improvement and in-depth exploration.Considered as a new feasible way of improving saline alkali land,which is environmentally friendly and cost-effective,AM technology has been widely concerned by researchers at home and abroad for its great potential application in global sustainable agriculture and environmental protection.In this paper,the physiological and molecular mechanism of improving salt tolerance of E.angustifolia by AMF(Rhizophagus irregularis)was studied by pot culture.The main results are as follows:Firstly,under the condition of potted cultivation,R.irregularis can infect and colonize the root organs of E.angustifolia.The mycorrhiza colonization rate of seedlings,cuttage and tissue culture seedlings reached 90%-100%.R irregularis significantly increased the plant height and survival rate of the seedlings under the three ways of seedling raising,and significantly promoted the growth of the seedlings of E.angustifolia,E.angustifolia cutting seedlings and E.angustifolia tissue culture seedlings.Secondly,through the comparative study of height,basal diameter,biomass,growth parameters of functional leaves and symptoms of salt damage of E.angustifolia seedlings under salt stress of 0,100,200 and 300mmol·L-1,the results showed that salt stress had a significant inhibitory effect on the growth of E.angustifolia seedlings,but under salt stress,after inoculating R.irregularis,the plant height,basal diameter,biomass of root,stem and leaf,total biomass and leaf growth parameters of E.angustifolia seedlings were significantly improved,and the salt tolerance of E.angustifolia was significantly improved by inoculating arbuscular mycorrhizal fungi.Thirdly,the distribution of mineral ion absorption of mycorrhizal and non-mycorrhizal E.angustifolia was compared under salt stress of 0,100,200 and 300mmol·L-1.The results showed that inoculation of R.irregularis significantly increased the absorption of K+,Ca2+and Mg2+mineral ions by E.angustifolia seedlings at 0,100,200 and 300mmol·L-1,and the distribution of Na+ in leaves and Na+transport to the ground were limited,and the seedlings inoculated with AMF significantly increased the K+/Na+ratio,Ca2+/Na+ratio and Mg2+/Na+ratio in leaves,maintained a stable ion balance in the body of E.angustifolia and alleviated the damage of Na+ stress on plant cells.Forthly,under salt stress,R.irregularis decreased MDA accumulation in leaves of E.angustifolia seedlings under salt stress;mycorrhizal E.angustifolia seedlings had higher soluble sugar and proline content;R.irregularis increased SOD,CAT,APX and POD antioxidant enzyme activities in leaves of E.angustifolia seedlings.The inoculation of R.irregularis in the roots activated the antioxidant enzyme system,accumulated more soluble substances,improved the ability of osmotic regulation,eliminated the toxicity of ROS,and enhanced the salt tolerance of E.angustifolia seedlings.Fifthly,inoculated with R.irregularis,the photosynthesis of E.angustifolia seedlings under salt stress was significantly increased:such as photosynthetic parameters(Pn、Tr、Gs、Ci),light responsive curve parameters(Pnmax、LSP、LCP、AQY)and water use efficiency of E.angustifolia.Inoculating R.irregularis effectively improved the light resources and water use status of E.angustifolia seedlings under salt stress,maintained a high photosynthetic rate,kept the normal photosynthesis of plants,and effectively alleviated and improved the salt tolerance of E.angustifolia seedlings.Lastly,the protein expression profiles of AMF-E.angustifolia symbionts induced by salt stress were significantly different.The root proteome of E.angustifolia seedlings treated with different methods was determined by LFQ proteomics and the results showed that:277 AM symbiotic salt-tolerance related DAPs were screened,of which 34 were up-regulated,37 were down-regulated,83 were not expressed and 123 were new proteins.241 AM symbiotic salt-tolerance related DAPs are mainly involved in single organ metabolism,lipid metabolism,cell membrane,catalytic activity and transferase activity.The symbiotic protein of mycorrhizal tolerance to salt stress is involved in metabolism,environmental information processing,genetic information processing,cell process and other metabolic pathways.The adaptive mechanism of salt stress response of mycorrhizal E.angustifolia may have the following three aspects:firstly,regulating the expression of AS,GOT,PAL,CCR,UER1 and COMT key enzymes,enhancing the host plant’s salt stress in terms of tryptophan synthesis,ammonia assimilation,carbon transport,K+/Na+concentration balance,scavenging active oxygen and free radicals,production of secondary metabolites such as lignin,indole and alkaloids,and cell wall formation to improve the salt tolerance of E.angustifolia;secondly,regulating the expression of PLD,DGK,SMT,GPAT,MINPP and other key enzymes of lipid metabolism can help host plant E.angustifolia in protein kinase signal transduction,cell membrane structure stability,regulation of lipid composition dynamic balance,auxin transport and distribution,plant growth and development,polyunsaturated fatty acid content,steroids signal molecules,calcium signal transduction,phosphoinositide signal system stability,guard cell ion pump and other aspects in response to salt stress;thirdly,GMPP,a key enzyme regulating the metabolism of amino sugar and nucleotide sugar,was differentially expressed to enhance the salt tolerance of the host plants of E.angustifolia in terms of promoting cell wall formation and AsA synthesis.In this research,the mechanism of salt stress tolerance of mycorrhizal E.angustifolia seedlings was analyzed from the perspective of physiological indexes and proteomics of plant stress resistance.The research results provide a theoretical basis for the use of AMF and salt tolerant plants to restore saline alkali land. |
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