Carbon And Nitrogen Metabolism And Response To Low Temperature Stress Of Medicago Ruthenica

Medicago ruthenica has rich germplasm resources with strong abiotic stress resistance,which could provide excellent genetic resources for forage breeding.Low temperature is one of the important factors affecting the plant growth,development,yield and quality.Carbon and nitrogen metabolism are the basic metabolism of plants,and play the important role in plant growth,development and resistance to abiotic stress.Therefore,the relationship study on carbon and nitrogen metabolism and cold resistance is of great significance to reveal the molecular regulation mechanism and to improve legumes varieties in M.ruthenica.In this study,the differences of main agronomic traits were compared in different M.ruthenica materials in two experimental fields,and the carbon and nitrogen metabolism pattern of leaves,stems and root crowns were revealed at different growth stages and during overwintering period,and the relationships were explored between the substance accumulation in root crown and yield,overwintering rate.The cold resistance mechanism study by the field experiment and temperature-controlled experiment was explored further comprehensively and systematically from the physiological level,biochemical level,molecular level,metabolite level and metabolic pathway.The main results were as follows:1.The fresh weight,depth,diameter,perimeter,mean number of vessels and phloem thickness of root crown were positively correlated with the fresh weight of aboveground biomass in two experimental fields of M.ruthenica.The differences of the agronomic traits were mainly caused by the hereditary property of all materials.There are high levels of carbon and nitrogen metabolism in soil with high value of p H,C/N and water content,and the stem/leaf ratio,height and fresh weight of aboveground biomass were relatively high.2.The content of main carbon and nitrogen compounds in root crown increased continuously from branching period to pod-bearing period,and the soluble sugar content in leaves and stems was relatively high in flowering period in all M.ruthenica materials.There are positive correlation relationships between the depth,diameter,perimeter,fresh weight,soluble protein content,free amino acid content,SS activities of root crown and the overwintering rate.The physiological and biochemical indexes and relative expression levels of MRHSP70,MRHLH and MRPP2C in root crown and root responded to the naturally reduced temperature during the overwintering and temperature-controlled stress by different change levels in all M.ruthenica materials.The low temperature significantly increased activities of SS and GS,the percentage content of carbon and nitrogen,δ¹³C andδ¹⁵N in leaves,shoots and roots and the ratio of underground biomass to aboveground biomass of M.ruthenica（L.）Trautv.cv.’Zhilixing’.3.The lipids,flavonoids,amino acids and their derivatives,and the transcription factors of ERF,b HLH and MYB families played the important roles in response to low temperature in M.ruthenica（L.）Trautv.cv.’Zhilixing’.The number of DEGs and the KEGG enrichment degree of pathways increased with the prolongation of low temperature stress treatment time.The DEGs and differential metabolites mainly enriched in metabolic pathways related to metabolic pathways,biosynthesis of secondary metabolites,carbohydrate metabolism,lipid metabolism and amino acid metabolism.4.Low temperature stress mainly affected the pathways of amino acid metabolism and carbohydrate metabolism of M.ruthenica（L.）Trautv.cv.’Zhilixing’,and the DEGs were highly correlated with the differential metabolites involved in these two pathways.The GS1、GSH2、BMY1、SUS6、BAM3、AMY3 gene,L-valine,L-leucine,proline,D-trehalose,D-sucrose and other small molecular compounds played the important role in adjustment mechanism of adaptability to freeze stress in M.ruthenica（L.）Trautv.cv.’Zhilixing’.