A biochemical study of the growth of Drosophila melanogaster

Abstract

Abstract1. The growth of a wild strain of Drosophila melanogaster has been studied from the time of hatching from the egg to the adult. Wet and dry weights, protein and protein fractions, lipids, RNA and DNA have been determined at successive intervals. 2. All estimates have been carried out on animals grown axenically on defined medium. The medium has been shown to permit growth which is as fast as on live yeast medium when the larvae can burrow freely. 3. Insoluble protein and chitin nitrogen reach a maximum of about 70% total nitrogen in the late pupa, at which time the soluble nitrogen reaches its lowest level. The amino acid fraction reaches a maximum in the early third instar. 4. The water content declines from 70–75% of the live weight at the end of the first instar, rises to a maximum during the second instar and declines sharply to about 66% at the prepupal stage. 5. Total lipids represent an increasing proportion of body weight during larval growth, increasing from about 6% in young larvae to about 15% at pupation. 6. The curve of RNA increase follows the dry weight and protein curves during larval life. The ratio of RNA to protein declines during the first two instars. 7. The increase in DNA content follows a path similar to that of RNA. The RNA/DNA ratio reaches a maximum 24 hours after hatching from the egg, declines to about half this value by 84 hours, and remains more or less constant thereafter. 8. The rates of increase of protein, RNA and DNA during successive periods of larval life show striking differences. For protein the rate is high and increasing until about 36 hours after which it declines rapidly during the rest of larval life. For both nucleic acids the rate of increase falls to a minimum in the early third instar, about the time of the critical size, then increases during proliferation of the imaginal discs and finally declines at the end of larval life. 8. The data are compared with evidence from other strains of Drosophila and from other species of insect. In the latter case, it appears that all the Diptera, so far examined, follow a similar trend in the increase of the nucleic acids during growth. 9. RNA synthesis has been followed during development from egg to adult with the aid of pulse‐labeling and sucrose gradient analysis. Developmental stages differ in the amount of rapidly labeled high molecular weight material which is most evident in newly hatched larvae and in mid‐third instar larvae, at times when the rate of synthesis of total RNA is high.