Cytological Development of Ascosphaera Atra

Abstract

Cytological studies of Ascosphaera atra were carried out using light and transmission electron microscopy (TEM). As mycelial growth becomes extensive, short lateral hyphal branches develop at irregular intervals near the growing tips of vegetative hyphae. Nuclei from vegetative hyphae migrate into these lateral processes, multiply, and disperse within terminal and subterminal cells formed by the development of two septa. Cyst primordia are multinucleate. Nuclei enter the cyst through a pore in the septum separating the terminal and subterminal cells. Nuclei migrating into the cyst are contained within an elongated membranous inclusion that develops one or more septa. Nuclei undergo repeated divisions within the developing cyst, and some of them appear to govern a process of spore formation that is characteristically observable as the association of a mitotically dividing nucleus with an area of homogeneous, nongranular, nonmembrane-bound cytoplasm. This area of cytoplasm develops into sporeballs. There is no evidence of Woronin bodies, ascogenous hyphae, croziers, or asci at the light or TEM level. Ascosphaera atra does not fit into the emended ordinal description of Ascosphaerales proposed by Skou.