Submitted to: Sugar Journal
Publication Type: Trade Journal
Publication Acceptance Date: May 7, 1999
Publication Date: N/A
Interpretive Summary: Sucrose metabolism is both a blessing and curse for the sugar industry. Sucrose metabolism is all the biochemical and physiological processes responsible for sucrose accumulation and degradation in the sugarbeet root. The unique aspects of sugarbeet sucrose metabolism allow sucrose to accumulate in the root at levels not seen in other crop plants. Sugarbeet roots typically accumulate sucrose to levels of 16-18% of the root's fresh weight. This ability to store sucrose to such levels is the basis of the sugarbeet industry. Sucrose metabolism, however, also involves sucrose degradation. Sucrose degradation is necessary to provide for the metabolic and material need of the plant, but it also causes sucrose losses during sugarbeet development and postharvest storage. Sucrose metabolism, therefore, both benefits and harms the sugarbeet grower and processor.
Technical Abstract: Sugarbeet roots accumulate sucrose to levels not found in any other crop plant. Sugarbeet roots typically contain 16-18% sucrose at harvest. The accumulated sucrose is the end product of sucrose metabolism. The final sucrose level is determined by all the biochemical and physiological processes involved in sucrose synthesis, transport and degradation. Sucrose synthesis begins with CO2 fixation in the leaves to produce glucose and fructose phosphates. These sugar derivatives are converted to sucrose by the action of sucrose phosphate synthase and sucrose phosphatase. Sucrose can be utilized by the leaf or transported vertically to the growing shoot tip or the root. Sucrose transported to the root is either utilized for the metabolic and material needs of the root or sequestered in the vacuole of root parenchyma cells for storage. Sucrose degradation largely occurs by the action of invertases or sucrose synthase. The invertases catalyze the hydrolysis of sucrose to glucose and fructose. These are two classes of invertases, acid invertase and neutral or alkaline invertase, based on their pH optimum for activity. Sucrose synthase, the other major sucrose degrading enzyme, catalyzes the reversible breakdown of sucrose to UDP-glucose and fructose.