Electron-microscopic study of glycogen in chick embryo liver

Abstract

A comparative study of thin and of contiguous thick sections of chick embryo liver was made. Small periodic acid—Schiff (PAS) positive areas as seen with the light microscope in thick sections probably contain glycogen, since previous digestion by means of salivary diastase renders these areas PAS negative. In the electron microscope these areas show a rather typical fine structure. They contain small membrane-bounded vesicles and located between them, small (20–33 m μ ) granules. Infrequently only the vesicular elements are seen, whereas a homogeneous material of low electron density appears in lieu of the granules. These granules and the homogeneous material are considered to represent glycogen. The reason for this variable appearance of the glycogen is not understood at present. The possibility that the Golgi complex plays a role in glycogen formation within these liver cells is discussed. Attempts were made to establish whether the Golgi region is PAS positive. The available evidence, although not conclusive, tends to show that it is not. This would seem to exclude the possibility that small granules seen within Golgi vacuoles are glycogen, but it does not rule out the possible role of the Golgi complex in glycogen formation. It is suggested that within the Golgi vacuoles an accumulation of glycogen precursors or of enzymes necessary for glycogen synthesis occurs and that such substances are subsequently discharged from the vacuoles into the surrounding cytoplasm.