An ultrastructural analysis of the changes in organelle arrangement and structure between the various spore types of Saprolegnia

Abstract

Serial-section analysis of synchronous spore populations of a species of Saprolegnia show that the organelles of primary and secondary zoospores undergo a sequence of changes in both arrangement and morphology during the change from motile spores to cysts and vice versa. The morphological changes include elongation and shortening of mitochondria, reversible stacking of endoplasmic reticulum cistemae, and formation and use of bars and newly described K bodies. These observations show that considerable synthetic and assembly activity occurs in the various spore stages. All organelles remain in characteristic locations in the motile spores but most become randomly arranged in the cysts, thus demonstrating the existence of some unsuspected and as yet undefined morphogenic cytoplasmic components. The functional implications of the described changes are discussed.