Salt Tolerance Evaluation And Its Mechanism Study For Maize Germplasm In Cold Region At Seedling Stage

The increasing level of soil salinization has gradually become a major environmental factor affecting plant growth and restricting productivity.Maize is an important food,feed,economic and industrial raw material in the world.Identifying and screening salt-tolerant maize germplasms and cultivating salt-tolerant maize varieties,illuminating the salt-tolerant mechanism of maize at seedling stage is an effective strategy to utilize saline land and improve the total yield of maize,which is of great significance for agricultural development.In this study,the 242 maize inbred lines was identified and classified according to the degree of salt tolerance in Heilongjiang Academy of Agricultural Sciences from 2011 to 2017.Salt tolerant inbred lines and salt sensitive inbred lines were selected as experimental materials to analyze the photosynthesis,antioxidant system,nitrogen metabolism,ion content,osmotic adjustment and transcription,to explore the differences of salt tolerance mechanism.The results provided technical support and theoretical basis for the selection of salt tolerant maize cultivars,and the development and utilization of saline soil.The main results are as follows:1.With clustering analyses,242 maize inbred lines at seedling stage was classified into five groups: 12 of 242 were highly salt-tolerance,e.g.“B46”;42 of 242 were medium salt-tolerance,e.g.“NC320”;58 of 242 were generally salt-tolerance,e.g.“50K-4-1”;77 of 242 were salt-sensitive,e.g.“H0480”;53 of 242 were highly salt-sensitive,e.g.“NC236”.2.Under low concentration(55 mmol/L)salt stress,the contents of chlorophyll in maize inbred lines were increased.Compared with NC236,the contents of chlorophyll in the leaves of B46 increased significantly.With the increase of Na Cl concentration,the contents of chlorophyll in two maize inbred lines decreased,and the decrease of B46 was less than that of NC236.B46 showed stomatal limitation in the range of Na Cl concentration from 0 to 165 mmol/L,non-stomatal limitation in the range of 220 mmol/L;NC236 showed stomatal limitation in the range of Na Cl concentration from 0 to 110 mmol/L,and non-stomatal limitation in the range of Na Cl concentration from 165 to 220 mmol/L.Compared with NC236,the decreasing amplitudes of the maximum photochemical efficiency(Fv/Fm),the potential photochemical efficiency(Fv/Fo),the photochemical quenching coefficient(q P)and the initial fluorescence(Fo),andincreasing amplitude of the non-photochemical quenching coefficient(NPQ)of B46 were less under salt stress.3.Compared with NC236,the contents of As A and GSH,and ratios of As A/DHA and GSH/GSSG of salt-tolerant inbred line B hong-2 decreased slightly,which beneficial to maitain low contents of superoxide anion(O2-),hydrogen peroxide(H2O2),malondialdehyde(MDA)and relative conductivity(EL)under Na Cl stress.4.Compared with NC236,B46 had a smaller decrease in contents of NO3–and NO2–,and a smaller increase in NH4+content.Under salt stress,the maximal GS and GOGAT activities of salt-tolerant maize inbred line B46 appeared at Na Cl concentration of 110 mmol/L,and the maximal GS and GOGAT activities of NC236 appeared at Na Cl concentration of 55 mmol/L;the maximum activities of NADH-GDH and NAD-GDH appeared at 165mmol/L Na Cl concentration for B46,and at 110 mmol/L Na Cl concentration for NC236.The decreases of GOT and GPT activities were less in B46 than NC236 under Na Cl stress.5.Under salt stress,compared with NC236,the contents of Pro,soluble protein and soluble sugar in B46 increased significantly;the variation amplitudes of Na+content,K+content and K+/Na+in B46 were less than NC236.Under Na Cl stress,B46 had higher contents of IAA in leaves and Z+ZR in leaves and roots and lower ABA content in leaves and roots than NC236.6.A total of 3524 and 6000 DEGs were generated under salt stress in the salt-sensitive and salt-tolerant inbred lines,respectively.Furthermore,1856 upregulated and 2008 downregulated DEGs were specific to the salt-tolerant inbred line,some of which may be involved in resistance to salt stress and enhanced salt tolerance.Gene functional annotation and enrichment analysis indicated that terms related to photosynthesis and responses to stress were significantly enriched in the downregulated and upregulated genes,respectively,for both genotypes,while terms related to biosynthetic processes,metabolic processes and catabolic processes were specifically enriched in the upregulated genes in B46.The DEGs involved in the abscisic acid(ABA),ethylene,jasmonic acid(JA)and salicylic acid(SA)signal transduction pathways may determine the difference in salt tolerance between the two varieties,especially one central component Sn RK2,that positively regulates ABA signaling and was only upregulated in B46.Analysis of DEGs related to ROS scavenging showed that some peroxidase(POD),glutathione S-transferase(GST),catalase(CAT)and superoxide dismutase(SOD)genes specific to L87 probablyenhanced its salt tolerance.The analysis of transcription factors(TFs)in response to salt stress indicated that the WRKY TFs might be involved in plant salt tolerance and related to plant resistance.