Submitted to: American Society of Sugarbeet Technologists
Publication Type: Proceedings
Publication Acceptance Date: March 22, 1999
Publication Date: N/A
Interpretive Summary: The domestic sugarbeet crop is valued at more than 1.2 billion dollars and provides more than 50% of the sugar produced in this country. In a world of increasing global competition and declining commodity prices, increases in productivity are imperative for the sugarbeet industry to remain viable. An understanding of the mechanism for sucrose losses during sugarbeet growth and postharvest storage would greatly aid this effort. The major enzymes responsible for sucrose degradation are acid invertase, neutral or alkaline invertase, and sucrose synthase. A research strategy has been devised to determine the relative importance of these enzymes in sucrose losses during the growth and development of the sugarbeet root and during its postharvest storage. The objective of these studies is to understand the biochemistry and physiology of sucrose losses in sugarbeet roots with the goal that this knowledge may lead to changes in cultural or storage practices, or genetic improvement to increase extractable sucrose from roots.
Technical Abstract: It has long been known that the major enzymes involved in sucrose catabolism in plants are the invertases and sucrose synthases. The role of these enzymes in sucrose losses in sugarbeets during growth and development and postharvest storage, however, is unclear. Past studies have provided conflicting results as to the relative importance of these two enzymes in sucrose loss in sugarbeet. These conflicts may arise from the nature of the enzymes involved. In most plants, invertase and sucrose synthase are not single enzymes, but families of enzymes consisting of several isoforms. It is likely that the different isoenzymes of an enzyme family perform different functions and are important at different development stages. Enzyme activity assays however, typically measure total activity for the family, not the individual isoenzymes. The objective of ongoing studies at the Northern Crop Science Laboratory in Fargo, ND is to determine the relative role of the individual isoenzymes for sucrose catabolism by comparing their activity relative to sucrose content and respiration. Total sucrose synthase activity, soluble and insoluble acid invertase activity and alkaline invertase activity will be measured in relation to carbohydrate content and root respiration. Activity of the individual isoenzymes will then be determined using activity staining of isoelectric focusing or nondenaturing protein gels and RT-PCR. This approach will be used to examine the role of sucrose synthase and invertase isoenzymes during growth and development and postharvest storage.