Submitted to: Archives of Insect Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 26, 2000
Publication Date: N/A
Interpretive Summary: The silverleaf whitefly (Bemisia argentifolii) is a major agronomic pest on a variety of crop species including cotton. Whiteflies feed on plant sap, obtaining a diet rich in sugar. The main sugars in plant sap are glucose and fructose, which are chemically linked to form the common table sugar, sucrose. For whiteflies to use sucrose as a nutrient, they must be able to break the chemical bond that links glucose and fructose. Previous studies have shown that whiteflies contain an enzyme called alpha-glucosidase that breaks sucrose into its constituent sugars. In the present study, we characterized this enzyme and examined the effects of an inhibitor of the enzyme on sugar uptake, metabolism and excretion. We showed that whiteflies contain multiple forms of alpha-glucosidase. These different forms are probably located in different parts of the whitefly. We found that an inhibitor of alpha-glucosidase caused whiteflies to excrete much less of the sugar they ingested, probably because the inhibitor blocks the activity of a specific alpha- glucosidase. The study provides new insights into the location, properties and function of a key enzyme necessary for whitefly nutrition. Understanding the biochemical elements of whitefly nutrition may lead to new methods for control of this insect pest.
Technical Abstract: The involvement of alpha-glucosidase in the partitioning of ingested sucrose between excretion and incorporation was investigated in the silverleaf whitefly (Bemisia argentifolii). Approximately half of the alpha-glucosidase activity in adult whiteflies was soluble and the remainder was associated with membranes. In contrast, almost all of the trehalulose synthase was membrane-associated. Bromoconduritol, an inhibitor of glucosidases, inhibited trehalulose synthase and alpha- glucosidase activities in whitefly extracts. Addition of bromoconduritol to artificial diets decreased the extractable trehalulose synthase and alpha-glucosidase activities by about 30 and 50%, respectively and reduced the amount of carbohydrate excreted by about 80%. Ingestion of bromoconduritol did not affect respiration, the content and distribution of soluble carbohydrates in whitefly bodies or the conversion of labeled sucrose into glucose, trehalose and isobemisiose. The results indicate that partitioning of ingested carbon between excretion and metabolism in whiteflies is highly regulated, probably involving multiple forms of alpha-glucosidase that facilitate a separation of the processes involved in the metabolic utilization of sucrose and those involved in excretion of excess carbohydrate.