Effect of the alpha-glucosidase inhibitor, bromoconduritol, on carbohydrate metabolism in the silverleaf whitefly, Bemisia argentifolii

The involvement of a-glucosidase in the partitioning of ingested sucrose be tween excretion and incorporation was investigated in the silverleaf whitef ly (Bemisia argentifolii). Approximately half of the alpha -glucosidase act ivity in adult whiteflies was soluble and the remainder was associated with membranes. In contrast, almost all of the trehalulose synthase was membran e-associated. Isoelectric focusing revealed that soluble and membrane-assoc iated alpha -glucosidases were each composed of several isozymes in the pH 5 to 6.5 range, but the distribution of activity among the various isozymes was different. Bromoconduritol, an inhibitor of glucosidases, inhibited tr ehalulose synthase and alpha -glucosidase activities in whitefly extracts. Inhibition was greatest when bromoconduritol was incubated with extracts pr ior to the addition of sucrose, consistent with the irreversible nature of this inhibitor. Addition of bromoconduritol to artificial diets decreased t he extractable trehalulose synthase and alpha -glucosidase activities by ab out 30 and 50%, respectively. Ingestion of bromoconduritol reduced the amou nt of carbohydrate excreted by about 80% without changing the distribution of the major honeydew sugars or causing an increase in the proportion of su crose that was excreted. Ingestion of bromoconduritol did not affect respir ation, the content and distribution of soluble carbohydrates in whitefly bo dies, or the conversion of labeled sucrose into glucose, trehalose and isob emisiose. The results indicate that partitioning of ingested carbon between excretion and metabolism in whiteflies is highly regulated, probably invol ving multiple forms of alpha -glucosidase that facilitate a separation of t he processes involved in the metabolic utilization of sucrose from those in volved in excretion of excess carbohydrate. Published 2001 Wiley-Liss, Inc.