Effect of 20-hydroxyecdysone on the ultrastructure of the posterior silk gland cells in the silkworm Bombyx mori

By means of electron microscopy, the effect of oral administration of 20-hydroxyecdysone (MH) on the ultrastructure of the posterior silk gland cells in the silkworm Bombyx mori was investigated. The result showed that the posteruor silk gland cells were very sensitive to MH treatment and immediate conspicuous changes would appear in the shape and structure of the nuclei as well as the development of organelles in the cytoplasm. The changes differed with the time of treatment and the MH dosage. The treatment with medial dosage (4 mu g/larva) enhanced the formation and development of the organelles related to silk protein synthesis and promoted cellular growth, while the treatment with higher dosage (8-16 mu g/larva) would result in the earlier formation of lysosomes in the early fifth larval instar. MH treatment in the intermediate and late stages of the fifth instar could on one hand enhance further development of the rough endoplasmic reticulum and other organelles and on other hand bring forth the occurren