A reevaluation of the mitotic spindle pole body cycle in Tilletia caries based on freeze-substitution techniques

Abstract

Mitosis in the wheat pathogen Tilletia caries (Basidiomycota, Tilletiales) was investigated by electron microscopy of serially sectioned, fast-frozen, freeze-substituted mitotic cells called ballistospores. A duplicated spindle pole body consisting of two identical, three-layered globular elements connected by a middle piece was attached to the extranuclear face of each nucleus at interphase. During mitosis, astral and spindle microtubules radiated from the globular elements that form the poles of an intranuclear spindle. At metaphase, chromosomes were interspersed with the nonkinetochore microtubules, and they were spread along the central two-thirds of the spindle. Each chromatid was attached to a spindle pole by a single, continuous, kinetochore microtubule. Postmitotic replication of the spindle pole body occurred during late telophase to interphase. Results from this study are presented in the form of a model of the mitotic spindle pole body cycle in Tilletia, and this model is compared with the one previously reported for Tilletia and other basidiomycetes. Key words: electron microscopy, freeze substitution, mitosis, spindle pole body, Tilletia.