Identification Of Heat Tolerance And Analysis Of Heat Acclimation Effect Of Wheat Cultivars And Related Species

The global warming caused by the intensification of greenhouse effect has made the modern agricultural production system face severe challenges,and the high temperature has seriously affected the yield and quality of wheat.The screening and identification of heattolerant germplasm resources and the breeding of heat-tolerant cultivars are important for coping with the high temperature climate and ensuring high and stable wheat yields.In this study,wheat cultivars and relatives of different ploidy were selected for the basal and acquired heat tolerance identification,and materials with significant differences in acquired heat tolerance were screened.The effects of heat acclimation on wheat growth,physiological characteristics and gene expression of HSPs were further examined to provide a basis for the selection and breeding of heat-tolerant wheat cultivars and the study of heat tolerance mechanism.The results of the study are as follows:1.Optimization of techniques for the identification of basal heat tolerance and acquired heat tolerance in wheatThree wheat cultivars with different heat tolerance were selected and tested under different seedling ages,heat acclimation conditions and high temperature stress conditions to determine changes in seedling growth index.An optimized technique for the identification of basic and acquired heat tolerance in wheat was established(7 days of sand cultivated wheat seedlings were treated at 44℃ for 5 h to evaluate the basal heat tolerance,after 2 h of heat acclimation at34℃ and 3 h of recovery at 20℃,the acquired heat tolerance was evaluated by high temperature treatment at 44℃ for 5 h),and the results were highly significantly and positively correlated with the results of the identification of post-flowering dry heat wind resistance in wheat,which could well distinguish the differences in acquired heat tolerance of different wheat cultivars.2.Evaluation of basic and acquired heat tolerance of different wheat cultivars and relatived speciesUsing the established technique for the identification of basal and acquired heat tolerance in wheat,108 wheat materials of different ploidy were identified for heat tolerance.Cluster analysis based on heat tolerance coefficients for dry weight per plant and root length of wheat seedlings under high temperature stress(HT)and heat acclimation-recovery-high temperature stress(A-HT)to compare differences in basal and acquired heat tolerance.Eighteen wheat cultivars with strong basal heat tolerance,including SN23 and LY502,and eight other ploidy materials,including DW13 and DW18,were selected.Twenty-two wheat cultivars with strong acquired heat tolerance were obtained,including SN23 and TAM107,and 13 other ploidy materials were obtained,including 5AA23 and DW6.3.Effect of heat acclimation on physiological characteristics of wheat seedlings and expression of heat shock protein genesFour wheat materials with significant differences in basal and acquired heat tolerance were subjected to direct high temperature and heat acclimation-recovery-high temperature stress treatments,and leaves were sampled at 0 h,1 h,3 h and 5 h of heat stress to determine physiological and biochemical parameters.The results of measuring s HSP gene expression in leaves sampled at different times of heat acclimation and heat stress treatments showed that the expression of s HSP23.6,s HSP26.6and s HSP17.8 genes was significantly up-regulated under heat stress in SN23,which was closely related to its strong basal heat tolerance.The high level of s HSP23.6 and s HSP26.6gene expression during heat acclimation and subsequent heat stress was closely related to the strong acquired heat tolerance.5AA23 with the strong acquired heat tolerance was closely related to the highly significant induction of s HSP16.9 and s HSP17.8 gene expression by heat acclimation,which not only induced them rapidly,but also induced them at a very significantly high level.4.Effects of heat acclimation at flowering on physiological characteristics and the gene expression of s HSP in wheat plantsThree wheat cultivars with different heat tolerance were selected and subjected to heat acclimation at 34°C for 3 d after flowering at one day and heat stress treatment at 38°C/28°C for 10 d at 10 days after flowering.The results showed that heat acclimation treatment at flowering significantly alleviated the dry matter accumulation of seeds in SN23 and hunderdgrain weight of TAM107 of the heat-tolerant.The s HSP gene expression in the flag leaves at 3,6 and 9 d of heat stress treatment showed that heat stress at 10 d after flowering had significantly different effects on gene expression of four types of s HSP in wheat flag leaves.s HSP16.9 and s HSP26.6 gene expression were more affected by long term heat stress at 38°C,and there were significant differences between different heat-tolerant cultivars.