A REEVALUATION OF THE MITOTIC SPINDLE POLE BODY CYCLE IN TILLETIA CARIES BASED ON FREEZE-SUBSTITUTION TECHNIQUES

Mitosis in the wheat pathogen Tilletia caries (Basidiomycota, Tilletia les) was investigated by electron microscopy of serially sectioned, fa st-frozen, freeze-substituted mitotic cells called ballistospores. A d uplicated spindle pole body consisting of two identical, three-layered globular elements connected by a middle piece was attached to the ext ranuclear face of each nucleus at interphase. During mitosis, astral a nd spindle microtubules radiated from the globular elements that form the poles of an intranuclear spindle. At metaphase, chromosomes were i nterspersed with the nonkinetochore microtubules, and they were spread along the central two-thirds of the spindle. Each chromatid was attac hed to a spindle pole by a single, continuous, kinetochore microtubule . Postmitotic replication of the spindle pole body occurred during lat e telophase to interphase. Results from this study are presented in th e form of a model of the mitotic spindle pole body cycle in Tilletia, and this model is compared with the one previously reported for Tillet ia and other basidiomycetes.