Uptake and metabolism of leaf proteins by the silverleaf whitefly

To determine if plant proteins can be ingested and metabolized by the silverleaf whitefly, whiteflies were fed artificial diets containing either 35S-labeled cotton leaf proteins or a fluorescently labeled recombinant leaf protein. Confocal microscopy showed that whiteflies contained fluorescence throughout their digestive tracts and in their honeydew after feeding on fluorescently labeled protein. On diets containing radiolabeled protein, 35S was ingested and either excreted as amino acids or retained in the body in protein and free amino acids. The profiles of radiolabeled whitefly polypeptides were similar for whiteflies feeding on labeled protein and labeled amino acids. Thus, whiteflies can ingest plant proteins, degrade them to free amino acids, and either excrete the amino acids or use them for de novo protein synthesis. Uptake and metabolism of radiolabel occurred when whiteflies fed on 35S-labeled leaves. Honeydew from these insects contained a small amount of labeled protein. The label in honeydew protein was primarily associated with a 22.4 kDa polypeptide. This polypeptide co-migrated with a labeled whitefly polypeptide and its synthesis was inhibited by cycloheximide. The identity and function of this protein are unknown. Arch. Insect Biochem. Physiol. 39:155–165, 1998.