Ultrastructural Studies of Encystment and Germination in Phytophthora Palmivora

This study was undertaken to examine the ultrastructural organization of encysting zoospores, cysts, and germinating cysts of Phytophthora palmivora using the method of freeze substitution. During encystment, changes in the outer surface of the plasma membrane were accompanied by changes in organization of peripheral cisternae. Electron-opaque, vesicular structures and membrane-bound patches of cytoplasm were observed outside the plasma membrane at early stages of encystment. Dictyosomes and tubular vesicles, the latter believed to be derived from peripheral cisternae, were associated with many coated pits and coated vesicles throughout encystment. During germination, variously shaped apical vesicles were observed at the tip of the germ tube. These vesicles appeared to be derived from dictyosomes and it is suggested that their processing involves multivesicular bodies as an intermediate stage.