Ultrastructure and cytochemistry of glycogen-containing vacuoles in gastrodermal cells in developing hydranths of a hydromedusan coelenterate

Hydranth buds from the colonial hydroid Sertularia pumila (Hydromedusae) were observed by electron microscopy during their development. Before hydranth expansion, the gastrodermal columnar digestive cells had large numbers of vacuoles. These vacuoles contained many membranous components as well as α-glycogen and dense ring- and crescent-shaped bodies. The rings and crescents were not osmiophilic, but did react to periodic acid oxidation in the PA-TSC-SP test for carbohydrate. These structures were digestible by α-amylase and pullulanase. The chemical analyses and the close association of the rings and crescents to α-glycogen particles showed that they may be a highly condensed form of glycogen. Golgi bodies in association with the gastrodermal vacuoles had acid phosphatase activity. This enzyme was only slightly active in the vacuoles. It is suggested that the vacuoles arc primarily storage organelles with a potential for digestion.