Differential Responses Of Physiological And Transcriptome Analysis To Salt Stress And Alkali Stress In Capsicum

There were 23%saline soil and 37%soda soil around the world,and its distribution is expanding year by year.And nearly 1/3 is saline-alkali soil in Xinjiang which located inland with huge evaporation.It is generally believed that saline soil is mainly composed of neutral salts such as sodium chloride,while alkaline soil is mainly composed of sodium carbonate,with the pH is over than 9.0.Studies have shown that neutral salt stress and alkaline salt stress have different effects on plants,and plants have different adaptation strategies to the two stresses.In order to clarify the different effect of neutral salt and alkaline salt on the growth and development of pepper seedlings,the pepper was used as a test material to simulate the saline-alkali stress under hydroponic conditions.The differences of osmotic regulation,antioxidant properties,nitrogen metabolism,and transcriptional expression were analyzed of pepper seedling leaves under neutral salt?NaCl,pH7.05?,alkaline salt?Na₂CO₃:NaHCO₃=1:9,pH8.98?,and mixed salt?NaCl:Na₂CO₃:NaHCO₃=10:1:9,pH8.95?.In order to provide the reference for the cultivation of pepper in saline-alkali soil,the differential response mechanism of pepper seedlings to the stress of neutral salt,alkaline salt and mixed salt were expounded from the physiological and transcription levels.The specific results of this study were as follows:1.Compared with the control,the proline content of the pepper leaves increased under salt,alkali and mixed salt stress,the increase was the largest under neutral salt stress.The soluble sugar content of pepper leaves under alkaline salt and mixed salts stress were higher than the control,and the soluble sugar content decreased rapidly under neutral salt stress,which indicating that proline plays an important role in osmotic regulation of pepper seedlings under neutral salt stress,while soluble sugar tends to regulate alkaline salt stress caused by high pH.Under three stresses,pepper seedlings could increase the content of proline and soluble sugar by up-regulating the expression of P5CS and?-OAT genes under three kinds of salt stress and induce the expression of HKT,NHX,CS genes to affect the osmotic regulation of pepper seedlings.In addition,the expression of CS gene was inhibited after the three days of neutral salt stress,and it was always highly expressed in alkaline salt stress,which indicated that pepper leaves also resisted damage caused by high pH by significantly up-regulating the expression of the citrate synthase gene?CS?.Thus,it was reveal that citric acid plays a more important role to alkaline salt stress in pepper.2.The results of the determination of the content of ascorbi cacid?ASC?and glutathione?GSH?,antioxidant enzyme activity and expression of related genes in pepper seedlings under neutral salt,alkaline salt and mixed salts stresses showed that the pepper seedlings first eliminated excessive reactive oxygen species?ros?through the stable reduced ASC and reduced GSH in cells to maintained the REDOX balance.Glutathione reductase?GPX?activity and gene expression under alkaline salt stress were higher than that under neutral salt stress,indicating that alkaline salt stress was inclined to balance excessive reactive oxygen species by increasing the power of GSH library,so as to reduce oxidative damage.Meanwhile,the activity of antioxidant enzyme and the expression of relevant genes showed that the three stresses could inhibit the REDOX efficiency to different degrees,but the activity of SOD and CAT showed a more rapid response to the neutral salt stress,and the response to the alkaline salt stress mainly occurred in the late stage of the test.3.The analysis of nitrogen content,nitrogen metabolization-related enzyme activity and gene expression in pepper seedling under neutral salt,alkaline salt and mixed salts stresses showed that three salt stresses could reduce nitrate nitrogen content in pepper seedling leaves,and the up-regulated expression of nitrate transporter NRT2.5 in pepper leaves was induced to accelerate the transport of external nitrogen.The content of ammonium nitrogen increased significantly with time under the three stresses,and the content of ammonium nitrogen in pepper leaves under alkaline salt stress was significantly higher than that under neutral salt stress after 9 days of stress.Under stress,the enzyme activity of NR,GS and GOGAT in pepper leaves decreased,and the corresponding gene expression was also down-regulated.The above nitrogen metabolism results indicated that the nitrogen metabolism pathway of pepper seedling leaves was inhibited under the salt,alkali and mixed salts stress,and the destruction effect was stronger under the alkali stress at the same Na⁺concentration.4.Transcriptome sequencing of pepper seedling leaves under salt and alkali stress for 4 h,13 h,34 h and 58h yielded 203.32g high-quality data.The number of differentially expressed genes were 858,3121,1274and 2263 at each time point under neutral salt stress.The number of differentially expressed genes in alkaline salt stress were 601,3511,503 and 1075,and the number of differentially expressed genes in both types of salt stress peaked at 13 h.Through GO and KEGG enrichment analysis,it was found that the saline-alkali differential genes were mainly concentrated in photosynthesis,osmotic regulatory substances synthesis,REDOX process,nitrogen metabolism,organic acid metabolism and other processes.Eight genes were randomly selected for verification,and the experimental results were consistent with the sequencing results,which proved that the sequencing was relatively accurate.The sequencing results can be applied to subsequent studies.