Bemisiose: an unusual trisaccharide in Bemisia honeydew.

Homopteran insects feeding upon on plant phloem sugars excrete a syrup termed honeydew which contains high concentrations of oligosaccharides. The creation of these oligosaccharides from sucrose in the phloem sap by transglycosylation reactions’ has been proposed as an osmoregulatatory mechanism in these insects*. Understanding this osmoregulation process would require a knowledge of the carbohydrates involved, but very few detailed analyses of the oligosaccharides in these excretions exist. A recent analysis of the smaller sugars in honeydew from the silverleaf whitefly (BemSz argentifoh) honeydew showed that its most abundant saccharide component was the unusual disaccharide trehalulose3. In order to analyze this sugar mixture more completely, a gradient high-performance anion-exchange chromatography (HPAEC) analysis of Bemisiu honeydew was carried out which showed that this syrup was composed of N 30 components (Fig. 1) including an unknown sugar that constituted about 3% (peak area) of the total sugars in the mixture. Chemical-ionization and electron-ionization gas chromatography, enzyme digestion, and ‘H and 13C NMR experiments showed this saccharide to be a trisaccharide consisting entirely of cY-D-glucose residues. From these results, a structure was proposed for this oligosaccharide (Fig. 2) which is identical to a trisaccharide that has been recently synthesized4*5 but which has not been previously reported to occur in higher organisms. The common name “bemisiose” is suggested for this sugar because it was found in Berni.% honeydew. An HPLC analysis of a trifluoroacetic acid hydrolyzate of bemisiose, using an anion HPLC column6~7, showed that it consisted entirely of glucose. Methylated