Submitted to: American Society of Sugarbeet Technologists
Publication Type: Abstract Only
Publication Acceptance Date: 11/13/2000
Publication Date: N/A
Technical Abstract: Three enzyme activities are responsible for nearly all sucrose catabolism in sugarbeet roots. Acid invertase, alkaline invertase and sucrose synthase activities convert sucrose to the hexose sugars glucose, fructose and UDP-glucose. Activity stained isoelectric focusing gels were used to determine the number of isoenzymes that contribute to each of these activities. Sugarbeet roots contain at least two soluble acid invertase isoenzymes, an insoluble acid invertase activity, two alkaline invertase isoenzymes and two sucrose synthase isoenzymes. Each isoenzyme exhibited a unique pattern of developmental expression. Acid invertase isoenzymes were most active in the roots of young plants and were the predominant sucrolytic activity in roots of seedlings. Activity of the major acid invertase isoenzyme paralleled root growth rate and was inversely correlated to sucrose accumulation. The predominant sucrolytic activity during all but the earliest stages of growth was a sucrose synthase isoenzyme. A second sucrose synthase isoenzyme became evident as roots approached maturity. Nearly all sucrose accumulation and enlargement of the taproot occurred when sucrose synthase was the major sucrolytic activity. Alkaline invertase was a minor sucrolytic activity in sugarbeet roots and was present at all but the early stages of development. The different patterns of expression for the major sucrolytic isoenzymes of sugarbeet roots suggest that they are likely to have different functions in the developing root.