Effect of high temperature on the metabolic processes affecting sorbitol synthesis in the silverleaf whitefly, Bemisia argentifolii

Whiteflies accumulate the polyhydric alcohol, sorbitol, when exposed to tem peratures greater than about 30 degrees C. Feeding experiments using artifi cial diets containing labeled sucrose showed that more of the label was inc orporated into whitefly bodies and less was excreted in the honeydew when f eeding was conducted at 41 compared with 25 degrees C.;Analysis of the comp onents of the honeydew showed that more of the excreted label was in glucos e and fructose and less in trehalulose at 41 degrees C than at 25 degrees C . A similar effect of temperature on honeydew composition occurred for whit eflies feeding on cotton leaves. Measurement of the activities of glycolyti c, pentose-phosphate and polyol pathway enzymes at 30 and 42 degrees C show ed that NADPH-dependent ketose reductase/sorbitol dehydrogenase (NADPH-KR/S DH), sucrase,. glucokinase and glucose-6-phosphate dehydrogenase activities were stimulated to a greater extent at 42 degrees C than trehalulose synth ase sind fructokinase. NAD(+)-sorbitol dehydrogenase (NAD(+)-SDH) activity was inhibited at 42 degrees C. We propose that high temperature alters meta bolic activity in a way that increases the availability of fructose and sti mulates pentose-phosphate pathway activity, providing both the substrate an d coenzyme for sorbitol synthesis. High temperature also increases the acti vity of NADPH-KR/SDH, the enzyme in whiteflies that synthesizes sorbitol, b ut inhibits the activity of NAD(+)-SDH, the enzyme that degrades sorbitol. Published by Elsevier Science Ltd. All rights reserved.