Submitted to: Journal of Sugarbeet Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2001
Publication Date: N/A
Interpretive Summary: Sucrose catabolism influences the growth, development and sucrose content of sugarbeet roots. Three enzyme families contribute to sucrose catabolism in sugarbeet roots. Acid invertase, alkaline invertase and sucrose synthase degrade sucrose to invert sugars thereby providing the substrates needed for the growth and energy needs of the developing root. These enzymes also affect sucrose accumulation in the root. Sugarbeet roots were found to contain at least two soluble acid invertase isoenzymes, an insoluble acid invertase activity, two alkaline invertase isoenzymes and two sucrose synthase isoenzymes. Sucrose synthase was the predominant sucrolytic activity during most of development, primarily due to the activity of a single isoenzyme. The acid invertases were the predominant sucrose degrading activity in seedling roots, although their activity declined to nearly undetectable levels early in root development. Alkaline invertase was a minor sucrolytic activity throughout development. Parallels between a soluble acid invertase isoenzyme and growth rate, and a sucrose synthase isoenzyme and sucrose accumulation suggest that these enzymes may play a role in the production of high yielding, high sucrose content sugarbeet roots.
Technical Abstract: Sugarbeet roots contain at least seven different sucrolytic activities throughout their development. Two soluble acid invertase isoenzymes, an insoluble acid invertase activity, two alkaline invertase isoenzymes and two sucrose synthase isoenzymes have been identified. Each enzyme had a unique pattern of developmental expression. Soluble and insoluble acid invertase activities were the predominant sucrolytic activity in roots of young seedlings and declined rapidly as the root aged. Soluble acid invertase activity was due primarily to the activity of a single isoenzyme. A second minor isoenzyme of soluble acid invertase was evident only in the earliest stages of development. High soluble and insoluble acid invertase activities were found concurrent with a rapid growth rate, high glucose levels and minimal sucrose accumulation. Sucrose synthase was the major sucrolytic activity during most of the root's development. One sucrose synthase isoenzyme was present throughout development. A second isoenzyme was evident as the roots approached maturity. Nearly all sucrose accumulation and enlargement of the taproot occurred when sucrose synthase was the predominant sucrolytic activity. Alkaline invertase was a minor sucrolytic activity, and was present at low relatively constant levels at all but the earliest stages of development. The relationship of these sucrolytic isoenzymes to growth, sink strength and sucrose storage in sugarbeet roots is discussed.