Electron Microscopic Studies on the Posterior Silk Gland of Silkworm, Bombyx mori (I)
Development and Maturation of the Posterior Silk Gland of 5th Instar Larvae
1966 Volume 18 Issue 3 Pages 160-173
Details
1966 Volume 18 Issue 3 Pages 160-173
Development and maturation during the 5th instar larvae of the posterior silk gland of silkworm, Bombyx mori, have been studied electron microscopically. For convenience, development of the gland could be discussed in terms the of following four phases.
( 1 ) The first or lag phase (5th instar 0-12 hours). The ultrastructure of the posterior silk gland cell during this phase is essentially similar to that in later moulting stage of the 4th instar. Rough endoplasmic reticulum is not well developed and many free ribosomes are observed.
( 2 ) The second or proliferation phase (5th instar 24-96 hours). The silk gland starts to grow very rapidly. Especially rough endoplasmic reticulum proliferates explosively, and the cytoplasm is filled with large lamellar endoplasmic reticulum. Concentric lamellar structure (whorl structure) of endoplasmic reticulum is occasionally found around at 96 hours.
( 3 ) The third phase or the stage of fibroin biosynthesis (5 th instar 96 hours-fully maturated larvae). Proliferation of rough endoplasmic reticulum is followed with the biosynthesis of fibroin. Lamellar endoplasmic reticulum is now transformed to tubular or vesicular endoplasmic reticulum, the cavities of which become enlarged, probably filled with synthesized fibroin. Golgi vacuoles, Golgi vesicles, and secretion granules also increase in number.
( 4 ) The fourth phase or cytolytic phase (fully maturated larvae-pupal ecdysis). The morphological change in the last phase of the 5th instar larvae is quite different from the previous three phases and will be described in the second report of this series.
