Ultrastructural studies of the life cycle of Physarum flavicomum grown in pure culture

The purpose of the investigation was to study, at the ultra- structural level, the various stages and the transitional changes between stages of the life cycle of Physarum flavicomum var. 1 grown in pure culture. Plasmodia and microplasmodia contain similar cytoplasmic components and exhibit the extracellular slime coat. Their granular cytoplasm consists of the following organelles and inclusions: nuclei, tubular type mitochondria with nucleoid-like regions, vacuoles containing pigment granules, slime materials and foreign substances, cytoplasmic fibrillar bands, lipid inclusions, free ribosomes and B-glycogen granules. However, the ectoplasmic region of microplasmodia is larger than in migrating plasmodial fans. Vacuoles containing slime materials are greater in 'slime phase' microplasmodia than in actively growing microplasmodia and plasmodia. Micrographs reveal that some of these slime vacuoles appear to be undergoing dehiscence, releasing their contents to the cell surface. Cytochemical evidence suggests that these vacuoles play an important role in the formation of the surface slime. 'Slime phase' microplasmodia lack the large ectoplasmic region and fibrillar bands common to growing microplasmodia.