| Late spring coldness is an important meteorological factor limiting high and stable yield of wheat in wheat areas of Huanghuai and middle and lower reaches of Yangtze River.Although many studies have been carried out on late spring coldness in wheat,the evaluation methods of late spring coldness resistance in wheat are still to be improved.Young ear is the most vulnerable organ to late spring coldness,and also the most direct organ to determine yield.However,the physiological mechanism of young ear response to late spring coldness is still unclear.Therefore,in this study,24 wheat varieties with different winter-spring characteristics were selected as test materials,and the artificial climate chamber was used to treat different intensity of freezing stress during the development of young ear to the anther connective stage,so as to explore the key traits that can reflect the resistance of varieties to late spring coldness.On this basis,the physiological mechanism of young ear response to freezing stress of different frost resistant varieties(frost resistant Jimai 22 and sensitive Xumai 33)was studied through physiological indexes and proteomies analysis,in order to provide theoretical basis for evaluation of late spring coldness resistance,cultivation regulation and genetic improvement of wheat.The main research results are as follows:1.Under different intensity of freezing stress,there were differences in the correlation between the frost resistance of young ear at the anther connective stage and the frost resistance of varieties in winter and spring and the frost resistance of leaves at the overwintering stage.Under the freezing stress of anther connective stage,there was no significant correlation between the freezing degree of leaf and young ear,and young ear was more sensitive to freezing stress.The y ield and total yield of main stem were mainly affected by panicle number and grain number,but had little correlation with grain weight.There was a close relationship between the frost resistance of the leaves at the anther connective stage,the frost resistance of the leaves at the overwintering period and the winter-spring characteristic of the varieties.The frostbite rate of young ear and leaf freezing index were significantly positively correlated with the yield decrease of main stem,while the correlation with the total yield decrease was significantly decreased.The primary ear(normal ear formation)and the regenerated ear(ear formation after the death of main stem and tiller)should be distinguished when the yield traits were used to evaluate the resistance to late spring coldness in wheat.The semi-winter varieties Jiangmai 816,Huaimai 20,Jimmai 22 and Lianmai 8 were selected,and the spring varieties Yangmai 15,Zhenmai 12 and Zhenmai 168 were selected.2.Under the freezing stress of anther connective stage the contents of MDA and H2O2 in young ear of wheat were significantly increased,and the activities of antioxidant enzymes SOD,CAT,POD,APX and the contents of antioxidant substance ASA were also increased to varying degrees.The content of GSH in young ear of Xumai 33 was significantly increased under the freezing stress of anther connective stage,but it was decreased in Jimai 22.The contents of soluble total sugar,sucrose,glucose and fructose in young ear of the two varieties increased under the freezing stress of anther connective stage.The contents of sucrose and fructose in Jimai 22 increased significantly,while those in Xumai 33 increased significantly.The activities of PK and PFK,the key glycolysis enzymes in young ear of the two varieties,were increased,but the content of ATP was significantly decreased under the freezing stress of anther connective stage.Through the analysis of the contents of 10 kinds of endogenous hormones,it was found that the overall levels of growth promoting hormones(IPA,K,IBA,ICA,etc.)showed a downward trend,while the contents of growth inhibiting hormones(ABA,JA,SA,ACC,etc.)showed an upward trend under the freezing stress of anther connective stage.Compared with Xumai 33,Jimmai 22 had higher activities of CAT and APX,contents of ASA,GSH,soluble total sugar,sucrose,fructose,ATP,and hormone levels of ABA,JA,SA and ACC at normal temperature.3.A total of 7998 proteins were identified in the young ear of Jimai 22 and Xumai 33 under the freezing stress of anther connective stage,among which 1071 differentially expressed proteins were identified between different varieties and treatments differential protein screening was performed at a differential multiple(FC=fold change)and p<0.05 threshold).Compared with normal temperature control,138 proteins were differentially expressed in young ear of Jimai 22 and 507 proteins were differentially expressed in Xumai 33 under freezing stress during the anther connective stage.Bioinformatics analysis showed that there were significant differences in the response of young ear of the two varieties to the freezing stress during the anther connective stage.However,compared with the normal temperature control,32 different proteins were co-expressed in the two varieties under the freezing stress of anther connective stage,which belonged to defensin,HIPP,ACO(promote ethylene synthesis),polygalacturonate-inhibiting protein(inhibit pectin degradation),peroxidase,etc.There were 481 differentially expressed proteins in the proteome of the young ear of the two varieties at different stages at room temperature,and these differentially expressed proteins were significantly enriched in catalytic activity,response to stress and response to stimulus.The number of different proteins in young ear of the two varieties was reduced by 24.32%under normal temperature by freezing stress.Bioinformatics analysis showed that the proteins differentially expressed in the young ear of Jimai 22 were enriched in the nucleosome assembly and tissue compared with those of Xumai 33 under the freezing stress of anther connective stage of nucleosome assembly,nucleosome organization,proteinDNA complex assembly and chromatin assembly and remodeling.A comprehensive analysis of the physiological and proteomic results showed that improving the scavenging capacity of ROS,accumulation of soluble sugar,improvement of cell wall traits and up-regulation of defensin protein expression were the important mechanisms of young ear response to freezing stress at the anther connective stage.Compared with Xumai 33,the young ear of Jimmai 22 had stronger defense ability against low temperature,and the young ear of Jimmai 22 could maintain higher transcription activity under freezing stress,which might be the main reason for the difference in frost resistance of young ear of different varieties at the anther connective stage. |
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