Studies on the nutrition of drosophila with particular reference to nucleic acid metabolism

Abstract

Aspects of the nutrition of Drosophila melanogaster (Meigen) have been investigated, particularly the role of nucleic acid in stimulating growth and pupation of larvae raised under axenic conditions. Chemically defined and partially chemically defined media were used. Full descriptions of the techniques employed in establishing axenic cultures of Drosophila larvae are given.No larval growth occurred on media containing 13 amino acids obtained from several British firms. It was suggested that traces of heavy metals as chemical contamination of these acids were responsible for the failure of larval growth.Oregon -K, a phenotypically wild -type stock that was reported to have been inbred for over 700 generations, was found to require nucleic acid for growth, although some growth occurred in the absence of nucleic acid or its constituents. The pyrimidine riboside, cytidine, was found partially to replace the whole molecule of ribonucleic acid. Adenine and guanine, the purine bases, accelerated the rate o larval growth and development but failed to allow more pupae to be formed. The presence of the pyrimidine base, uracil, permitted no growth of the larvae whatsoever. This result was interpreted as due to the toxicity of the compound rather than due to a metabolic inactivity.Attempts were made to localize on the chromosomes a genetic factor responsible for the requirement. All attempts failed to reveal the presence of such a single factor.In further attempts to localize the gene, a mutant marker stock was used which grew well on nucleic acid -less casein medium, but did not on a nucleic acid -less medium containing free amino acids. These results led to an investigation of the effect on larval growth of varying hydrogen -ion concentrations in casein and amino acid media. In (2LR)10d /Cy sp2 and Oregon -K, known to require nucleic acid in their diets, were found able to grow well on nucleic acid - less casein media provided the hydrogen -ion concentration was high. In (2LR)1Od /Cy sp2 failed to grow under similar conditions, but with free amino acids substituted in the medium for casein.Theoretical possibilities to explain the pH effect are presented and discussed. These suggest that the nucleic acid requirement in some Drosophila stocks may actually be a requirement for the acid amide of glutamic acid, glutamine, or some substance closely related to it, which would participate in purine and pyrimidine synthesis. It is further suggested that the presence of such a compound in a chemically defined medium would accelerate larval growth and development in all Drosophila stocks.