Lysosomes and Related Structures in the Posterior Silk Gland Cells of<I>Bombyx mori.</I> I. In Late Larval Stadium

Abstract

Measurements of lysosomal enzyme activities (acid phosphatase, acid RNase, and cathepsin) and observations of electron microscopic cytochemical preparations were correlated with ultrastructural changes in the posterior silk gland cells during the late larval stadium of the silkworm Bombyx mori. In the fourth instar the lysosomal enzymes were synthesized exclusively in the feeding stage when the wet weight of the gland increased exponentially, and the enzymes were probably stored in Golgi bodies. In the molting stage a number of autophagosomes, autolysosomes and autophagic vacuoles appeared in the cells, and the lysosomal enzymes presumably played pivotal roles in the catabolic processes of the silk gland cells. In the early half of the fifth instar (0-96 h), a similar exponential increase in lysosomal enzymes was observed, and the synthesized enzymes were also probably stored in Golgi bodies. In the middle of the fifth instar (96 h) when the metabolism of the silk gland was changed from the growth phase to stationary phase, several characteristic structures appeared, such as lipid droplets, myelin structures and whorl structures of rough ER. In the latter half of the fifth instar, the lysosomal enzyme activities were stabilized temporarily then increased again slightly arriving at a maximum value at the end of the fifth instar.