Morphological And Physiological Characterization And Transcriptomics Of Barley Root System Adaptation To Alkali Stress

Barley,as an important pioneer crop for saline alkali land improvement,is of great significance for the development and utilization of saline alkali land.In this study,two barley varieties with significant differences in alkali tolerance,Jia-HY460-6R（alkali-tolerant）and Hu90-6573（alkali-sensitive）,were selected as materials to analyze the morphological characteristics,antioxidant capacity,ion balance and osmotic regulation,as well as changes in root cell wall components of barley under alkali stress and reveal the morphological and physiological mechanisms of root damage caused by alkali stress.Through transcriptome analysis,the key candidate genes formed by the difference in alkali tolerance of barley were excavated,and the molecular mechanism of barley root response to alkali stress was revealed,providing a theoretical basis for the breeding of alkali tolerant barley varieties and the research of salt tolerant cultivation techniques.The main results are as follows:（1）With the advance of alkali stress time,the leaf relative water content and leaf water loss rate showed a decreasing trend,and the leaf relative water content and leaf water loss rate of Jia-HY460-6R were significantly higher than those of Hu90-6573;The leaf area extension rate（LER）showed a trend of first increasing and then decreasing,reaching its maximum value on the 6th day after stress.Moreover,on the 6th,10th,and 15th days after stress,the LER of adding HY460-6R was significantly higher than that of Hu 90-6573.There is a significant difference in the root to shoot ratio between the two varieties,Jia-HY460-6R showed continuously increasing,while the Hu 90-6573 reached its peak on the 6th day.The daily relative growth rate（RGR）of the roots and aboveground parts of the two varieties showed a trend of first increasing and then decreasing,reaching its maximum value on the 2th day after stress.At the 10th and 15th days,the RGR of the roots and aboveground parts in Jia-HY460-6R were significantly higher than those of Hu 90-6573.（2）Under alkaline stress,the root exudates of the two varieties showed a trend of first increasing and then decreasing,and the average root exudate of Jia-HY460-6R is 28.69%higher than that of Hu 90-6573.The root activity of Jia-HY460-6R showed a trend of first increasing and then decreasing,while the trend of Hu 90-6573 gradually decreased,and the average root activity of Jia-HY460-6R was 37%higher than that of Hu 90-6573.In addition,the activities of H⁺-ATPase and Ca²⁺-ATPase related to root activity were significantly higher than those of Hu 90-6573 at 6d,10d,and 15d after alkali stress.（3）With the extension of alkali stress time,the activity of SOD,POD,CAT,APX,GR,MDHAR,GPX and GXT and the value of GSH/GSSG and ASA/DHA of the two varieties were and CAT increased first and then decreased with the advancement of stress time,and the activity of APX and GR,the value of GSH,GSH/GSSG and ASA/DHA all showed a downward trend.The antioxidant enzymes and GSH/GSSG and ASA/DHA ratios of Jia-HY460-6R were significantly higher than those of Hu 90-6573.（4）Under alkaline stress,the Na⁺content and Na⁺/K⁺in shoots and roots of the two varieties were significantly higher than CK,and the increase of Jia-HY460-6R was significantly less than that of Hu90-6573.The contents of Fe²⁺and K⁺in shoots and roots were lower than those in CK,but in Jia-HY460-6R were significantly higher than those in Hu 90-6573.In addition,under alkaline stress,the osmotic adjustment substances such as soluble sugar content,soluble protein content and proline content of the two varieties increased first and then decreased,and at each stress time,Jia-HY460-6R was significantly higher than Hu90-6573.At the same time,starch,sucrose and the key enzymes related to synthesis increased first and then decreased with the stress time,and compared with the control,the increase of Jia-HY460-6R was significantly greater than that of Hu 90-6573.（5）Under alkali stress,the pectin,hemicellulose,lignin,pectin methylesterase,laccase,phenylalanine ammonia lyase and xyloglucan endotransglycosidase/hydrolase of the two varieties were higher than CK as a whole.As the stress time progressed,all indicators showed a trend of first increasing and then decreasing,and in Jia-HY460-6R was significantly higher than that of Hu 90-6573.（6）Compared with CK,3540,2760,6645 and 3568,6102,7813 DEGs were identified in Jia-HY460-6R and Hu90-6573 at 6h,2d and 6d under alkali stress,respectively.KEGG enrichment analysis of the above DEGs showed that Jia-HY460-6R is mainly enriched in pathways such as MAPK signaling pathway,biosynthesis of phenylpropanoid compounds,glutathione metabolism,starch and sucrose metabolism,nitrogen metabolism,and flavonoid biosynthesis,while Hu90-6573 is significantly enriched in starch and sucrose metabolism,biosynthesis of phenylpropyl compounds,MAPK signal transduction pathway,galactose metabolism.Under alkaline stress,DEGs between the two varieties were significantly enriched in pathways such as phenylpropanoid biosynthesis,starch and sucrose metabolism,glutathione metabolism,and MAPK signaling pathway.Based on the physiological characteristics of alkali tolerance,60 candidate genes related to alkali tolerance were screened by analyzing carbon and nitrogen metabolism,plant hormone related pathways,amino acid metabolism,MAPK signaling pathways,and ROS clearance related pathways.The above results indicate that alkali tolerant barley and alkali sensitive barley have different response genes in response to alkali stress,not regulated by a single gene or pathway, but by multiple metabolic pathways.