Inhibition of chitin biosynthesis in cultured imaginal discs: Effects of alpha-amanitin, actinomycin-D, cycloheximide, and puromycin.

Wing imaginal discs isolated from last instar larvae of the Indian meal moth,Plodia interpunctella, produced chitin when incubated in vitro with ≧2×10-7 M 20-hydroxyecdysone. Chitin biosynthesis was initiated 8 h after the conclusion of a 24-h treatment with hormone. Simulataneous incubation of wing discs with 20-hydroxyecdysone and either inhibitors of RNA synthesis (alpha-amanitin, actinomycin-D) or inhibitors of protein systhesis (cycloheximide, puromycin) prevented chitin biosynthesis. We conclude from our results that RNA and protein synthesis must continue undiminished during the hormone-contact period, and that synthesis of protein, but not of new RNA is required during the posthormone culture period. Our findings are consistent with the hypothesis that ecdysteroids stimulate insect metamorphosis by promoting the synthesis of new RNA and protein during a hormone-dependent phase followed by hormone-independent protein synthesis.