Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Proceedings
Publication Acceptance Date: 2/28/2000
Publication Date: N/A
Interpretive Summary: The yield of extractable sucrose is a major determinant of the value of the sugarbeet crop. Extractable sucrose yield is determined by the extent of sucrose accumulation during the growing season and the extent of sucrose losses during postharvest storage and processing. The role of the major sucrose catabolizing enzymes in these processes is the focus of a new study at the USDA/ARS Northern Crop Science Laboratory. Initial work has focused on the relative importance of acid invertases, alkaline invertase and sucrose synthase to sucrose losses during sugarbeet root development. The invertases, especially the acid invertases, are the predominant sucrose degrading activities in young sugarbeet roots. By six weeks of growth, however, their contribution to the total sucrose degrading activity of roots is minimal. Sucrose synthase is the major sucrose degrading activity in sugarbeet roots after six weeks of growth and remains the major sucrose degrading activity until harvest.
Technical Abstract: Developmental changes in the activities of the major sucrose catabolizing enzymes of sugarbeet roots were determined. In seedling roots the acid invertases were the predominant sucrolytic enzymes. Soluble and insoluble acid invertase activities were greatest in two week old sugarbeet roots. After two weeks, their activities dropped precipitously to nearly negligible levels. Soluble acid invertase activity was due to a single isoenzyme. Alkaline invertase activity was also greatest in two week old roots. Alkaline invertase, however, was present only at low levels throughout development. Two alkaline invertase isoenzymes were present at all developmental stages, but their relative contribution to total alkaline invertase activity changed with root development. Sucrose synthase was the major sucrose utilizing enzyme in sugarbeet roots six weeks of age or older. Two sucrose synthase isoenzymes contributed to sucrose synthase activity. Only one sucrose synthase isoenzyme was evident during the first twelve weeks of growth. Two sucrose synthase isoenzymes were present after sixteen weeks.