Effects Of Soaking Seeds With Salicylic Acid On The Alfalfa Growth And Development Under Saline-alkali Stress

Salinity-alkalinity of soil is a major environmental stress factor seriously affecting the seed germination and plant growth.In this study,we soaked the seeds of alfalfa by using exogenous salicylic acid,and performed the non-invasive testing to determine the ion fluxex in the apical meristem and elongation zone of alfalfa.To evaluate the seed germination,seedling growth,and physiological changes of alfalfa under salinity-alkalinity stress,the changes of metabolites,enrichment and expression profiles of the functional target genes of salicylic acid-mediated were investigated by the transcriptome sequencing,metabolome and qRT-PCR analyses.The seeds of the‘Gongnong NO.1'and‘Dongmu NO.1'alfalfa were immersed in the solutions of 0.5 mmol/L or 1 mmol/L of salicylic acid at room temperature for 24 hours,and transferred into the pots which are filled by the soils with highly salinity-alkalinity,and further cultured in the green house for 4 months.The seed germination rates,fresh weight,dry weight,plant height and root length were accordingly recorded,respectively,and also the chlorophyll,proline,soluble sugar,malondialdehyde and osmotic potentials in leaves were measured,respectively.Meanwhile,the treatment with salicylic acid of concentration of 0.5mmol/L was used for transcriptome sequencing and qRT-PCR.The alfalfa seedlings of one-month-old were selected to detect the Na~+,K~+and H~+ions fluxes in the root tip of the seedlings by non-invasive testing technique.The treatment with salicylic acid of 0.5 mmol/L was used for metabolome analysis.Data showed that soaking seeds of alfalfa with appropriate concentration of salicylic acid effectively increases the germination rates,plant heights,root length,fresh weight and dry weights of alfalfa seedings,and raised the accumulat ions of chlorophyll,proline and soluble sugar,and lowered the osmotic potentials and malondialdehyde contents in alfalfa leaves under salinity-alkalinity stress,thereby improving ions balance in leaves.Transcriptome sequencing and metabolome analyses revealed that‘Gongnong NO.1'and‘Dongmu NO.1'alfalfa had total of 31 and 123 of the differentially expressed genes,respectively,and‘Dongmu NO.1'exhibited that a total of 241 of the differential metabolites were co-expressed by the mediation of salicylic acid of 0.5 mmol/L,and these partial differentially expressed genes and metabolome are involved in the molecular functions and metabolic pathways.Salicylic acid soaking alfalfa seeds could lower the damage of the salinity-alkalinity to the plants and promote the alfalfa growth's development in response to salinity-alkalnity stress.The treatment of salicylic acid of 0.5 mmol/L was identified to have the best effect in enhancing the salinity-alkalinity tolerance.As exogenous signal molecules,salicylic acid significantly participates in the regulation and enrichment of the functional genes,and beneficial changes of differential metabolites of salicylic acid-mediated are involved in the regulation of metabolic pathways associated with stress resistance,and positively contribute to enhancing the salinity-alkalinity tolerance.This study suggests that a reasonable application of exogenous salicylic acid is an effective pathway in improving alfalfa planting in soils with salinity-alkalinity,and also provides a scientific reference for revealing the regulatory mechanism of salicylic acids-mediated under salinity-alkalinity stress.