Preliminary Study On Sucrose-decomposing Enzymes In Sweet Potato Root Expansion And Quality Formation

In order to clarify the role of sucrose catabolism in root tuber enlargement and quality formation of sweet potato,soluble sugar and starch contents and sucrose metabolic phases of four sweet potato varieties including starch-processed sweet potato(Baishu),fresh-eating and quality-type sweet potato(Guoshu),quantitative-type sweet potato(Xin xiang),fresh-eating and processing sweet potato(Sushu 17)were studied before and after root tuber formation and at different developmental stages after root enlargement.The activity of related enzymes was measured and analyzed.The findings of this study are as follows:(1)Sucrose-decomposing enzymes directly affect the composition and content of starch and soluble sugar from the early stage of tuber expansion to the late stage of tuber expansion,thus affecting the quality of sweet potato tubers.Invertase mainly plays a role in the early stage of tuber swelling,and has a greater impact on the composition and content of soluble sugar,while sucrose synthase mainly plays a role in the late stage of tuber swelling,and has a greater impact on starch content.At the early stage of root tuber enlargement,CWIN activity of cell wall invertase was positively correlated with sucrose and soluble sugar content,while Sus activity of sucrose synthase was negatively correlated with soluble sugar content and positively correlated with starch content.Sus activity was negatively correlated with sucrose and soluble sugar content,and positively correlated with starch content in the middle stage of root expansion.In the late stage of tuber expansion,the activity of cytoplasmic invertase CIN was positively correlated with the content of soluble sugar in tuber,while the activity of Sus was negatively correlated with the content of soluble sugar in tuber.and positively correlated with starch.The soluble sugar content of Fresh-eating sweet potato is higher than that of starch-processing sweet potato because its CWIN activity is higher than that of starch-processing sweet potato at the early stage of expansion,and the vacuolar invertase VIN activity of Fresh-eating sweet potato is higher at the early stage of expansion and its VIN activity decreases less than that of starch-processing sweet potato;while the starch content of starch-processing sweet potato is higher than that of Fresh-eating sweet potato because Sus activity is significantly higher than that of Fresh-eating sweet potato at each Type sweet potato.(2)Sucrose catabolism activity affected the direction of adventitious root differentiation in sweet potato:CIN regulated the whole process of adventitious root differentiation into tuber root;CWIN promoted adventitious root differentiation into fibrous root;VIN and Sus promoted fibrous root expansion into tuber root.High CWIN activity in adventitious roots of quantitative-type sweet potatoes can promote cell division;VIN with high activity in quantitative-type sweet potatoes can regulate cell osmotic potential and promote cell volume expansion;US with high activity in quantitative-type sweet potatoes affects cellulose synthesis and participates in cell construction;high CIN activity in quantitative-type sweet potato roots is likely to promote fineness by regulating the ratio of hexose to sucrose.Cell growth.These high activity sucrose decomposing enzymes make adventitious roots differentiate into more tubers than weight-type sweet potatoes.(3)The development degree of sweet potato pericap determines the size of tuber roots,and the main sucrose decomposing enzyme affecting the swelling of sweet potato skin at the later stage of development is CWIN.The higher the activity of CWIN,the larger the tuber roots at harvest stage.In the late stage of tuber enzymatic expansion,CWIN with higher activity of heavy sweet potato pericap could continue to decompose sucrose for the development of tuber enlargement.The number of sweet potatoes stopped enlarging because of its inadequate CWIN activity.In conclusion,sucrose catabolism plays an important role in root tuber development of sweet potato.It not only affects root tuber formation and yield(including quantity and size),but also affects its quality(starch and soluble sugar content).