Submitted to: American Society of Sugarbeet Technologists
Publication Type: Proceedings
Publication Acceptance Date: 3/21/2001
Publication Date: N/A
Interpretive Summary: Sugarbeet roots contain a number of enzymes that degrade sucrose. These enzymes are important for root growth, root development and sucrose partitioning to the root, and therefore influence the yield and sucrose content of the sugarbeet crop. Three families of enzymes, acid invertase, alkaline invertase and sucrose synthase, are responsible for nearly all degradation of sucrose in sugarbeet roots. To better understand their function during sugarbeet root development, the number of isoenzymes that contribute to each enzymes family was determined. The relative contribution of each isoenzyme activity to the total sucrose degrading capability of the sugarbeet root was also determined throughout development and in relation to root growth and sucrose accumulation. These studies revealed that sucrose synthase activity was the predominant sucrose degrading activity throughout most of root development and may be important for the regulation of sucrose partitioning to the root. Sucrose synthase activity was due to two isoenzymes. Acid and alkaline invertase activities were minor sucrose degrading activities during most of development. Acid invertase activity, however, was an important activity in early development and may be important for the rapid growth observed in young roots.
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. Sugarbeet roots contain at least two soluble acid invertase isoenzymes, an insoluble acid invertase activity, two alkaline invertase isoenzymes and two sucrose synthase isoenzymes as determined by activity staining of isoelectric focused polyacrylamide gels. Ease isoenzyme exhibited a unique patten 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.