Isobemisiose: an unusual trisaccharide abundant in the silverleaf whitefly, Bemisia argentifolii

The major soluble carbohydrates in the silverleaf whitefly, Bemisia argenti folii, were glucose, alpha,alpha -trehalose and an unknown sugar. Analysis of the unknown sugar and its chemical and enzymatic digestion products by h igh-performance liquid chromatography (HPLC) showed that it was probably a trisaccharide, consisting entirely of glucose, and containing both alpha,al pha -trehalose and isomaltose moieties. Matrix-assisted laser desorption ma ss spectrometry, mass spectrometry and C-13 and H-1 nuclear magnetic resona nce spectroscopy confirmed that the sugar was a trisaccharide with the foli o wing structure: O-alpha -D-glucopyranosyl-(1-->6)-O-alpha -D-glucopyranos yl-(1<->1)-alpha -D-glucopyranoside. This trisaccharide, found primarily in the bodies of B. argentifolii and not in their honeydew, is structurally s imilar to bemisiose [O-alpha -D-glucopyranosyl-(1-->4)-O-alpha -D-glucopyra nosyl-(1<->1)-alpha -D-glucopyranoside], a sugar first identified in Bemisi a honeydew. Consequently, the common name isobemisiose is proposed for the newly identified sugar. Isobemisiose, which has not been previously reporte d to occur in nature, constituted as much as 46% (w/w) of the ethanol-solub le sugars in adult B. argentifolii, equivalent to approximately 10% of thei r dry weight. It was also found in similar quantities in immature B. argent ifolii. Isobemisiose was detected in two other whitefly species and in seve ral species of aphids, but at lesser concentrations than in B. argentifolii . Labeling and pulse-chase experiments using [C-14]sucrose supplied to B. a rgentifolii in an artificial diet revealed that label accumulated in and wa s chased from isobemisiose more slowly than for either glucose or trehalose . Incubation of isobemisiose with cell-free extracts of B, argentifolii dem onstrated that these whiteflies contained the necessary complement of enzym es to fully degrade isobemisiose to glucose. These labeling and digestion e xperiments indicate that isobemisose is probably a storage carbohydrate in B. argentifolii. Published by Elsevier Science Ltd.