Effect And Mechanism Of Inoculated With Bacillus Pumilus On The Growth And Active Components Of Glycyrrhiza Uralensis Grown Under Drought Stress

Objective:In this paper,Glycyrrhiza uralensis Fisch.was used as research material to investigate the regulation effect of Bacillus pumilus on the growth and active components under drought stress,and to reveal its regulatory mechanism.Methods:The growth experiment of G.uralensis by indoor sand-bearing seedlings and outdoor culture pots were conducted to study the effects of inoculated with B.pumilus under drought stress on the growth parameters,stress physiological indexes,carbon and nitrogen metabolism,active ingredients and glycyrrhizic acid synthesis enzyme gene expression at different growth stages.Results:1.Indoor experiment results:inoculated with B.pumilus significantly increased the root length,stem length,number of lateral roots and leaves of G.uralensis seedlings under drought stress,and significantly increased the carbon metabolism related enzymes such as INV,SS,and SPS,the nitrogen metabolism related enzymes GOGAT and GDH and the contents of NO₃^-,NH₄⁺,soluble sugar,soluble protein,and free amino acid in the aerial parts of G.uralensis seedlings under drought stress.It is showed that the inoculation of B.pumilus could promote the carbon and nitrogen metabolism of G.uralensis seedlings and promote growth.Inoculated with B.pumilus significantly increased the expression levels of Gu SQS1 and Gu?-AS genes in the subterranean part,but decreased the expression levels of Gu HMGR,Gu SQS1 and Gu?-AS genes in the aerial parts,increased the content of underground glycyrrhizic acid,and reduced aboveground glycyrrhizic acid.It is indicated that the inoculation of B.pumilus can regulate the synthesis of glycyrrhizic acid by regulating the expression level of related enzymes in the process of glycyrrhizic acid synthesis,causing its content to change,and this regulatory effect is spatially selective.2.The outdoor potting experiment results:inoculated with B.pumilus significantly promoted the root length,increased the total fresh weight,total dry weight,root dry weight,root fresh weight,stem dry weight and leaves dry weight of of G.uralensis under drought stress,and increased active ingredient content including the contents of total flavonoids and total polysaccharides in roots,total polysaccharidesinstems,totalflavonoids,totalsaponinsandtotal polysaccharides in leaves,and contents of glycyrrhizin,glycyrrhizic acid,isoliquiritigenin,glycyrrhizone and glycyrrhetinic acid in roots,and up-regulates the gene expression levels Gu HMGR,Gu SQS1 and Gu?-AS.It was indicated that the inoculation of B.pumilus promoted the growth of G.uralensis and the accumulation of effective components,and increased the content of glycyrrhizic acid by regulating the expression of key enzyme genes in glycyrrhizic acid synthesis.Inoculated with B.pumilus decreased the H₂O₂ content and O₂^-production rate by increasing the activities of antioxidant enzymes GPX,CAT and GR and the contents of non-enzymatic antioxidants GSH and As A,thereby alleviating the membrane lipid peroxidation damage caused by drought stress,and finally the MDA content and membrane permeability were significantly reduced;inoculation with B.pumilus increased the content of soluble sugar and prevented the loss of water to achieve water conservation.Inoculated with B.pumilus maintained normal chloroplast morphology,clear and complete thylakoid membrane structure,and increased the activities of NR,GS,SS and SPS,chlorophyll content,photosynthetic rate;transpiration rate,stomatal conductance,intercellular CO₂ concentration and water use efficiency.The results indicated that B.pumilus inoculation can improve the photosynthesis and water use efficiency by maintaining intact chloroplast structure,increasing chlorophyll content,and carbon and nitrogen metabolic enzyme activities,thereby increasing the resistance of G.uralensis under drought stress and maintaining its normal growth.Conclusion:The mechanism of inoculation with B.pumilus under drought stress in enhancing the growth and active components of G.uralensis may be:B.pumilus can relieve oxidative damage,reduce osmotic pressure,increase net photosynthetic rate,and then increase carbon and nitrogen metabolism and water use,finally improved the growth and active ingredients accumulation of G.uralensis;through up-regulation of the expression of related enzymes in the glycyrrhizic acid biosynthesis process,and then promote the synthesis and accumulation of glycyrrhizic acid.