Effects Of Post-Heading High Temperature On Some Quality Traits Of Malt Barley And Its Molecular Mechanisms

High temperature or heat stress caused by global change has been become a major abiotic stress affecting crop yield and quality.Understanding the influence of high temperature on crop yield and quality formation and its mechanisms is helpful for developing the crop cultivars with high abiotic stress and optimizing the cultivation practices fighting against the stresses.Barley is a major cereal crop,with multiple utilization and wider adaptation.Currently,malt quality deterioration caused by high temperature occurres frequently in the world,and it is still unclear about the expression regulation of the genes related to malt quality traits in response to the stress.In this study,the main quality traits were determined on the two malt barley cultivars(ZU9 and Hua30)grown in the growth chambers with different temperature.Meanwhile we also measured the relative expression of the relevant genes using qRT-PCR,in order to reveal the physiological and molecular mechanisms of high temperature on malt barley quality.The main results obtained are as follows.1.Effect of post-heading high temperature on yield traits of ZU9 and Hua30In this study,we investigated the impact of one-week heat stress(32/26?,day/night)initiating from the 7th(HT7)and 14th(HT14)days after heading on grains per spike,seed setting rate and kernel weight.There were significant differences in these yield components among the treatments and between the two cultivars.Grains per spike and seed setting rate were higher for ZU9 than for Hua30 under both control and high temperature conditions.There was no significant difference in kernel weight between the two cultivars under normal condition(without high temperture treatment,NT),but ZU9 showed much more decline than Hua 30 under HT7 and HT14.In comparison with normal temperature(24/18?,day/night),heat stress significantly reduced kernel weight,seed setting rate,grains per spike for the two cultivars,with HT7 having a larger effect than HT14.2.Effect of post-heading high temperature on malt quality of ZU9 and Hua30Grain protein content increased significantly under HT7 and HT14,with HT7-treated plants showing the larger changes.Although there was no significant difference in grain protein content between ZU9 and Hua30 in control,the difference was significant in HT7 and HT14,with Hua30 having greater increase than ZU9.Moreover,?-glucan content also increased markedly after post-heading high temperature,with HT14 having a larger effect than HT7 and ZU9 being larger than Hua30.?-glucan content was consistently higher in Hua30 than that in ZU9 in all treatments.The contents of the four protein components increased significantly under post-heading high temperature,with HT7 having larger effect than HT14,but the increased extent varied greatly among protein components.In addition,there was also the difference between ZU9 and Hua30 in the responses of four protein components to high temperature.In addition,post-heading high temperature resulted in a significant increase in the activities of ?-amylase and LD,with HT7 having a greater effect than HT14,which is consistent with the response of protein content to post-heading high temperature.Moreover,the relative activity of the two starch hydrolases in Hua30 increased much more than that in ZU9.3.Effect of post-heading high temperature on the relative expression level of HvCslF6?HvCslF9?HvBmy1 and LD geneIn this study,we selected HvCslF6,HvCslF9,HvBmy1 and LD gene as key synthetic genes for malt quality traits.Post-heading high temperature significantly increased the relative expression levels of all four key genes,with HT7 having a greater effect than HT14.The expression up-regulation of key genes induced by post-heading high temperature led to the increase of ?-glucan content,?-amylase and LD activity.In addition,the differernce existed between ZU9 and Hua30 in the responses of all 4 gene expressions to post-heading heat stress.