The Single Mitochondrion, Fine Structure, and Germination of the Spore of Blastocladiella emersonii

SUMMARY: The motile spore of the water fungus, Blastocladiella emersonii, contains a single, large, posterior, eccentrically disposed mitochondrion; some 6–12 prominent, strongly osmiophilic, lipid-like organelles, bordered by a double membrane, occur along its outer edge. A single flagellum with the classical 9-plus-2 fibrillar structure is attached by at least one banded rootlet to the mitochondrion. The nuclear cap (a package of ribosomes) overlies the nucleus and is separated from it by a double membrane. The cytoplasm is somewhat granular, contains structures believed to be organelles (previously described as γ particles), but is devoid of any obvious cytoplasmic reticulum. Before spore germination, the flagellum undergoes a series of characteristic movements. Following this, the nuclear apparatus rotates through some 270°, but the spore itself does not turn. The flagellum is then retracted into the cell. Subsequently, the spore germinates by formation of a germ tube and the nuclear cap disintegrates.