Ultrastructural and cytochemical studies of zoospores, cysts, and germinating cysts of Phytophthora palmivora

Studies have been made of the ultrastructure and cytochemistry of zoospores, cysts, and germinating cysts of Phytophthora palmivora. The bulk of the zoospore cytoplasm is occupied by lipid bodies, crystalline vesicles containing lipid plus other unknown material(s), and granular vesicles containing protein. During a 6-h motile period after zoospore release no noticeable changes occur in crystalline and granular vesicles or in lipid bodies. Granular vesicles are retained if encystment is caused by centrifugation or agitation, but few remain when zoospores encyst under undisturbed conditions. Cysts begin to germinate 15 min after encystment is complete. Granular vesicles begin to disappear 30 min after germination starts and the process is complete 60 min later. Crystalline vesicles and lipid bodies also begin to disintegrate 30 min after germination begins, resulting in osmiophilic network-like breakdown products. The breakdown of these products increases with time but is not complete 90 min after germination.