INTERACTION BETWEEN THE ADH AND ODH LOCI IN RESPONSE TO ETHANOL IN DROSOPHILA-MELANOGASTER

Six Drosophila melanogaster strains were constructed from two isofemal e lines. The strains had four allele combinations at the alcohol dehyd rogenase (Adh) and octanol dehydrogenase (Odh) loci, while all alpha-g lycerophosphate dehydrogenase (alpha Gpdh), malate dehydrogenase (Mdh) , and aldehyde oxidase (Aldox) alleles were identical Second-instar an d early and late third-instar larvae were exposed to different concent rations 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. Activi ty differences were observed between the two Adh genotypes: ADH(F) all ozyme had considerably higher activity than ADH(S). Exogenous ethanol resulted in the highest increase in ADH activity in the second- and ea rly third-instar stages. This ADH induction depended on the allele com bination at the Adh and Odh loci; e.g., in the strain having the Adh(S )-Odh(S) allele combination, increased ADH activity was observed only after exposure to 7.5% ethanol. ODH activities differed according to t he Odh genotypes, in that the ODHS allozyme had a higher activity than ODHF. ODH activities did nor appreciably respond to different ethanol treatments. All six strains had identical alleles at the Mdh and alph a Gpdh loci, but nevertheless, the responses of these enzymes to ethan ol 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 Adh(S) allele. In Adh(F) strains, however; exposure to 7.5% ethan ol resulted in a considerable decrease in MDH activity in the second-i nstar larvae. Correlations among the response variables showed that OD H activities were strongly associated with fresh weight and the activi ties of all other enzymes, except for ADH. ADH activity, however showe d a significant correlation only with alpha GPDH activity throughout t he larval life. Both MDH and ODH activities were found to be in strong negative correlation with ADH activity in the second-instar larvae. A t this most sensitive life stage, the metabolic response to ethanol is highly correlated.