Comparative Analysis On The Osmoregulatory Characteristics Of Glycyrrhiza Inflata And G.uralensis Under Salt Stress

Drought and soil salinization are two mojor environmental factors that have greatly limited the pasture and crop productivity.The xerophytes and halophytes have evolved stronger stress resistance during their long-term adaptation to extremely harsh environments.Glycyrrhiza uralensis and G.inflata,the two Glycyrrhiza plants with strong salt tolerance that belong to Leguminosae,are mainly distributed in extreme harsh environments,such as desertification and salinization regions in north China.Studies on the physiological and molecular mechanisms of their stress resistance will not only contribute to the cultivation,development and utilization of Glycyrrhiza plants,but also provide an important theoretical foundation for the genetical improvement of stress resistance in crops and forages.Osmoregulation is one of the important mechanisms for most plants,especially halophytes and xerophytes,to adapt to salt and drought stress,mainly through active absorption of inorganic ions and synthesis of organic osmoregulation substances to maintain the ability of cell water absorption and water retention.However,systematic studies on the distribution characteristics of major osmoregulation substances,as well as the response patterns of genes related to the synthesis of organic osmoregulation substances and the absorption and transport of inorganic ions under salt stress have not been reported.Therefore,in this study,the difference of salt tolerance between the seedlings of G.uralensis and G.inflata,and the difference of concentration of the main osmoregulation substances in different tissues were compared between these two Glycyrrhiza plants.Then the differences in the expression of genes related to absorption and transport of inorganic ions and synthesis of organic osmoregulation substances were compared using transcriptome analysis and RT-q PCR method.The main results are as follows:1.G.inflata displays stronger salt resistance,compared with G.uralensis.Both two Glycyrrhiza plants accumulated a large amount of organic and inorganic osmotic substances under salt stress.And compared with G.uralensis,G.inflata could enhance its osmoregulation ability by synthesizing more osmotic substances such as proline,betaine and soluble sugar in roots,retaining Na⁺and NO₃^-accumulation in roots,and increasing K⁺and Cl^-accumulation in leaves.2.Under salt stress,compared with that in G.uralensis,the expression of genes（including P5CS2,PEAMT1,Su Sy2,SPS2,MD,AMS,etc.）involved in the synthesis of organic osmotic substances in root of G.inflata was up-regulated,which is conducive to promoting the synthesis of proline,betaine and soluble sugar in its roots.The up-regulated expression of HKT1;1 and NHX1 in roots of G.inflata could improve the ability of Na⁺unloading from xylem and Na⁺compartmentation into vacuoles,and thus enhancing the retainment of Na⁺in roots of G.inflata.Meanwhile,compared with that in G.uralensis,the up-regulated expression of NRT1.1,NRT1.2,NRT2.4,NRT2.5,CLCa and CLCb in root of G.inflata could improve the ability of NO₃^-absorption and vacuolar NO₃^-compartmentation in its root.3.Under salt stress,compared with that in G.uralensis,the high expression of SKOR and SLAH3 in roots and CLCc in leaves would be conductive to facilitating K⁺and Cl^-loading into xylem,respecitively,and Cl^-compartmentation in leaves of G.inflata,and thus promoting more K⁺and Cl^-accumulated in leaves of G.inflata for osmoregulation.The above findings revealed the osmoregulation characteristics and related mechanisms of two Glycyrrhiza species,especially G.inflata with stronger salt resistance under salt stress.These results would provide an important theoretical foundation for the cultivation and utilization of Glycyrrhiza plants as well as the genetical improvement of stress resistance in legumes in desert region.