Uptake and metabolism of leaf proteins by the silverleaf whitefly

To determine if plant proteins can be ingested and metabolized by the silve rleaf whitefly, whiteflies were fed artificial diets containing either S-35 -labeled cotton leaf proteins or a fluorescently labeled recombinant leaf p rotein. Confocal microscopy showed that whiteflies contained fluorescence t hroughout their digestive tracts and in their honeydew after feeding on flu orescently labeled protein. On diets containing radiolabeled protein, S-35 was ingested and either excreted as amino acids or retained in the body in protein and free amino acids. The profiles of radiolabeled whitefly polypep tides were similar for whiteflies feeding on labeled protein and labeled am ino 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 pr otein synthesis. Uptake and metabolism of radiolabel occurred when whitefli es fed on S-35-labeled leaves, Honeydew from these insects contained a smal l amount of labeled protein, The label in honeydew protein was primarily as sociated with a 22.4 kDa polypeptide. This polypeptide co-migrated with a l abeled whitefly polypeptide and its synthesis was inhibited by cycloheximid e. The identity and function of this protein are unknown. (C) 1998 Wiley-Li ss, Inc.