Glycogen distribution in the larval salivary gland cells during the development of Drosophila melanogaster and Drosophila auraria: an ultrastructural cytochemical study

Abstract

In this study, glycogen distribution during the development of larval salivary glands in two Drosophila species (D. melanogaster and D. auraria) was examined using the osmium tetroxide–potassium ferrocyanide technique at the ultrastructural level. Glycogen particles are found in big clumps in the salivary gland cells of D. melanogaster during the early third instar, mainly at the basal part of the cells; they are also found as scattered particles in the cytoplasm and very close to the apical plasma membrane during the secretory activity at this developmental stage. During the middle third instar, where the production of ‘glue’ secretory granules begins, glycogen particles are mainly scattered and they are seen near the Golgi complexes and secretory granules. No glycogen particles are seen during the late third instar and secretion of ‘glue’ secretory granules. Re-formation of glycogen begins after spiracle eversion. In the larval salivary gland cells of D. auraria, glycogen particles (scattered and in clumps) are seen in every developmental stage. In the larval fat body cells of both species, many huge clumps of glycogen particles are seen, independent of the developmental stage. These results indicate that glycogen provides an important source of energy during development of Drosophila salivary glands, but different species use glycogen at different metabolic pathways, according to their needs.