Submitted to: National Research and Action Plan for Silver Leaf Whitefly
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 1998
Publication Date: N/A
Technical Abstract: Accumulation of polyols in insects is well known as a cold-hardening response related to overwintering or to protection against cold shock. The whitefly is a major insect pest in tropical and subtropical regions where heat stress and desiccation pose formidable threats to survival. Sorbitol levels increased ten-fold when whiteflies were exposed to elevated temperatures. Sorbitol levels fluctuated diurnally under glasshouse and field conditions increasing 10-fold from morning to early afternoon. Feeding experiments on artificial diets showed that temperature and dietary sucrose concentration were key factors influencing sorbitol accumulation. Cell free extracts prepared from adult whiteflies catalyzed NADPH-dependent fructose reduction, but were unable to reduce glucose with either NADPH or NADH. Sorbitol synthesis in the whitefly was catalyzed by a novel NADPH- dependent ketose reductase. We cloned and sequenced a cDNA that encoded the eNADPH-KR/SDH to determine the primary structure of this unusual enzyme. Th cDNA encoded a protein of 352 amino acids with a calculated molecular mass of 38.2 kDa. The deduced amino acid sequence of the cDNA shared 60 and 41% identity with sheep and silkworm NAD+-dependent sorbitol dehydrogenases, respectively. We propose that the ketose reductase-mediated sorbitol accumulation is a mechanism for thermoprotection and osmoregulation in the whitefly, allowing the insect to thrive in environments conducive to thermal and osmotic stress.