Effects Of Dehydration Stress On Starch And Sucrose Metabolism In Postharvest Tobacco Leaves

In order to clarify the effects of different water loss treatments on starch and sucrose metabolism in post-harvest tobacco leaves,this experiment used flue-cured tobacco variety Qinyan 96 as the material,and set up no water loss treatment(CK),water loss 10%treatment(T1)and water loss 20%treatment(T2)of three water loss gradients.We analyzed the dynamic changes of starch content,sugar content,starch metabolism related enzyme activity and gene expression,sucrose metabolism related enzyme activity and gene expression in postharvest tobacco leaves,and explored the changes of starch and sucrose metabolism in tobacco leaves treated with dehydration stress.The results showed that:1.The analysis of starch metabolites content,amylase-related enzymes activity and gene expression showed that amylose degradation in post-harvest tobacco leaves was mainly concentrated in the early stage of dehydration(0-18 h),while amylopectin degradation was mainly concentrated in the late stage of dehydration(18 h).Compared with no water loss treatment,the starch content of post-harvest tobacco leaves treated with 10%water loss and 20%water loss was reduced by 30%and 14%respectively.The activities of AGP and GBSS in the water-treated tobacco leaves gradually decreased with the prolongation of post-harvest time,and the enzyme activities of the two treatments decreased rapidly in the later stage(after 12 h).In addition,the DBE activity and SBE activity of tobacco leaves showed a gradual decline with the prolongation of post-harvest time.In conclusion,the starch synthase activity of tobacco leaves was inhibited by dehydration stress treatment.Further gene expression analysis showed that the expression levels of AGP and GBSS increased firstly and then decreased with the prolongation of post-harvest time,indicating that starch anabolic inhibition was enhanced in the late(12 hours later),while the expression levels of DBE and SBE genes decreased with the post-harvest time(except SBE),so dehydration treatment inhibited starch synthesis in post-harvest tobacco leaves.The activity of amylolytic enzyme increased gradually with the prolongation of post-harvest time,and the expression of the corresponding enzyme gene increased.Combined with the change rule of starch material,it indicated that the dehydration stress treatment promoted the rapid degradation of starch content in post-harvest tobacco leaves and promoted the increase of soluble content.2.The content of sucrose metabolites,sucrose-related enzyme activities and gene expression analysis showed that compared with no water loss treatment,water loss treatment increased the content of soluble sugars such as sucrose,glucose and fructose in post-harvest tobacco leaves.The SPS activity of tobacco treated with 10%water loss decreased gradually with the prolongation of postharvest time,and the expression of SPS gene decreased,while the activities of SS and INV enzymes increased with the prolongation of post-harvest time,and the expression levels of SS and INV genes increased.The SPS,SS and INV activities and gene expression levels of tobacco treated with 20%water loss were opposite to those of 10%dehydration enzyme activity and gene expression.In summary,the tobacco leaves under the treatment of 10%water loss were mainly glucose catabolism after harvest,while the 20%water loss treatment inhibited the catabolism of sugar,but the treatment of water stress promoted the increase of sugar content in post-harvest tobacco leaves.In summary,from the different treatments on the enzymatic activity and gene expression of starch and sucrose metabolism in post-harvest tobacco leaves,the dehydration stress treatment inhibited starch anabolic enzyme activity and gene expression,promoted amylase activity and gene expression,and increased the degradation of starch;10%dehydration treatment promoted the activity and gene expression of sucrose catabolism,further decomposition of sucrose increased sugar content,while 20%dehydration treatment inhibited the activity and gene expression of sucrose catabolism,and reduced the increase of sugar content.The post-harvest tobacco leaves treated with water stress were better treated with 10%water loss.