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

Abstract

SUMMARYThe motile spore of the water fungus, BlatocladkZZu emersmii, 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 y 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.

Zoospore Germination in Blastocladiella emersonii: Cell Differentiation without Protein Synthesis?

“…The initial cell type, the zoospore, swims about by means of a posteriorly situated flagellum and can be maintained for relatively long periods in the absence of exogenous organic nutrients (3). The zoospore contains an impressively ordered array of internal organelles, but lacks a cell wall (1,4,5). Zoospore populations germinate upon exposure to any of certain monovalent salts (3,6).…”

An Albino Mutant of Blastocladiella emersonii: Comparative Studies of Zoospore Behaviour and Fine Structure

“…At the other extreme is the situation found in Blastocladiella emersonii and its derivatives : the regular appearance in unchilled zoospores of a doublemembraned nuclear cap that encloses essentially all its ribosomes, and (at least in some spores) additional small packets of ribosome-like particles, also delimited by double membranes but situated in the cytoplasm. Such satellite ribosome packages had not been seen (Cantino et al 1963)-or seen only very rarely (Reichle & Fuller, 1967;Lovett, personal communication)-by previous workers in spores from wild-type stocks of B. ernersonii, and it had not been determined whether they were connected to the cap or enclosed by separate membranes of their own. It is now known (Cantino & Mack, 1969) that they connect solely to the outer unit membrane of the nuclear cap's double membrane, and that they can be released as separate entities.…”

“…The enclosure of a zoospore's ribosomes in a membranous structure such as a nuclear cap apparently is not vital for all uniflagellate aquatic fungi; the motile spores of some Chytridiomycetes, for example, bear naked aggregates of ribosome-like particles either randomly distributed or localized around or near their nuclei, while others may enclose them only partially within loose networks of imperfect double membranes (Fuller, I 966 ;Chambers, Markus & Willoughby, 1967). And in the spores of Monoblepharella (Fuller & Reichle, 1968), ribosome-like bodies are found in two major areas: scattered at the cell's posterior, where they are not delimited by membranes; and closely packed around the nucleus, where they are partially delimited by flattened cisternae but otherwise in contact with cytoplasm.…”

“…Fine structure of wild-type and mutant zoospores Actively swimming wild-type zoospores of Blastocladiella emersonii are subglobose to ellipsoid. Numerous aspects of the fine structure of such spores have already been descril5ed (Cantino, Lovett, Leak & Lythgoe, 1963;Fuller, 1966;Lessie & Lovett, 1968). When spores were first released from dense populations of OC plants into a surface film of fluid on solid media, they were irregularly elongated rather than Spore structure in a Blastocladiella 375 smoothly ovoid and crawling amoeboids rather than active swimmers.…”

“…The significance of the differences among the granules situated in the doublemembraned lipid sac (Cantino et al 1963, Lessie & Lovett, 1968Reichle & Fuller, 1967) along the outer edge of the mitochondrion is still uncertain. In amoeboid as in swimming spores, these granules always appeared in two forms: one, an often elongated membrane-bound organelle (possibly a continuous matrix) of even electron density; the other, situated among the former, a somewhat polyhedral body with an electron-transparent centre and an electron-opaque limiting region.…”