Interaction between the Adh and Odh loci in response to ethanol in Drosophila melanogaster

Six Drosophila melanogaster strains were constructed from two isofemale lines. The strains had four allele combinations at the alcohol dehydrogenase (Adh) and octanol dehydrogenase (Odh) loci, while all alpha-glycerophosphate dehydrogenase (alpha Gpdh), malate dehydrogenase (Mdh), and aldehyde oxidase (Aldox) alleles were identical. Second-instar and early and late third-instar larvae were exposed to different concentrations of ethanol (0, 5, and 7.5%) and 3 days later fresh weights and the activities of ADH, ODH, alpha GPDH, and MDH were measured. Activity differences were observed between the two Adh genotypes: ADHF allozyme had considerably higher activity than ADHS. Exogenous ethanol resulted in the highest increase in ADH activity in the second- and early third-instar stages. This ADH induction depended on the allele combination at the Adh and Odh loci; e.g., in the strain having the AdhS-OdhS allele combination, increased ADH activity was observed only after exposure to 7.5% ethanol. ODH activities differed according to the Odh genotypes, in that the ODHS allozyme had a higher activity than ODHF. ODH activities did not appreciably respond to different ethanol treatments. All six strains had identical alleles at the Mdh and alpha Gpdh loci, but nevertheless, the responses of these enzymes to ethanol depended on the allele combinations at the Adh and Odh loci. alpha GPDH activity followed that of ADH in all experiments. MDH activities were not influenced by exogenous ethanol in the strains homozygous for the AdhS allele. In AdhF strains, however, exposure to 7.5% ethanol resulted in a considerable decrease in MDH activity in the second-instar larvae. Correlations among the response variables showed that ODH activities were strongly associated with fresh weight and the activities of all other enzymes, except for ADH. ADH activity, however, showed a significant correlation only with alpha GPDH activity throughout the larval life. Both MDH and ODH activities were found to be in strong negative correlation with ADH activity in the second-instar larvae. At this most sensitive life stage, the metabolic response to ethanol is highly correlated.