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

In this study, glycogen distribution during the development of larval saliv ary glands in two Drosophila species (D. melanogaster and D. auraria) was e xamined using the osmium tetroxide-potassium ferrocyanide technique at the ultrastructural level. Glycogen particles are found in big clumps in the sa livary 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 s ecretory activity at this developmental stage. During the middle third inst ar, where the production of 'glue' secretory granules begins, glycogen part icles are mainly scattered and they are seen near the Golgi complexes and s ecretory granules. No glycogen particles are seen during the late third ins tar and secretion of 'glue' secretory granules. Re-formation of glycogen be gins after spiracle eversion. In the larval salivary gland cells of D. aura ria, glycogen particles (scattered and in clumps) are seen in every develop mental stage. In the larval fat body cells of both species, many huge clump s of glycogen particles are seen, independent of the developmental stage. T hese 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.