Biochemical strategies of overwintering in the gall gly larva,Eurosta solidaginis: Effect of low temperature acclimation on the activities of enzymes of intermediary metabolism

Abstract

1. The activities of some enzymes of intermediary metabolism, including those involved in glycerol and sorbitol synthesis, were measured in the third instar larvae of the gall fly,Eurosta solidaginis sampled during a controlled (1°C per day decrease) low temperature acclimation of the larvae from 15 to 30°C. 2. Low temperature acclimation resulted in increased activities of three key enzymes of carbohydrate catabolism: phosphorylase, hexokinase and phosphofructokinase while other enzymes of glycolysis and the Krebs cycle were unaffected by low temperature acclimation. 3. Other enzymes whose activities were altered by low temperature acclimation included 3-hydroxyacyl-CoA dehydrogenase, an enzyme of fatty acid oxidation, glutamate dehydrogenase and glutamate-pyruvate transaminase. These latter two enzymes are involved in the synthesis of proline and alanine, amino acids which are accumulated in the larvae at low temperatures. 4. Polyol dehydrogenase activites catalyzing the NADPH-dependent reduction of glyceraldehyde, glucose or fructose were found inE. solidaginis as well as an NADH-dependent sorbitol dehydrogenase. The activities of both sorbitol dehydrogenase and polyol dehydrogenase were increased in the larvae with decreasing acclimation temperature, paralleling the production of sorbitol in these overwintering, freezingtolerant larvae. 5. The larvae displayed activities of phosphatases utilizing (in descending order of activity) glucose-6-P, fructose-6-P, glucose-1-P, glyceraldehyde-3-P, sorbitol-6-P and glycerol-3-P as substrates. Glyceraldehyde-3-P phosphatase showed a decrease in activity with decreasing acclimation temperature while the C6 sugar phosphate phosphatases showed a decreased activity only at the lowest, −30°C temperature. 6. The probable pathways for the synthesis of the cryoprotectant polyols, glycerol and sorbitol, inE. solidaginis are outlined and the control of intermediary metabolism during low temperature acclimation in these larvae is discussed.