The spindle pole body and postmeiotic mitosis in Auricularia fuscosuccinea

Abstract

Basidia of Auricularia fuscosuccinea were examined with the transmission electron microscope. The spindle pole body (SPB) at meiotic prophase I, interphase II, and prophase of postmeiotic mitosis consisted of two globular elements connected by a middle piece and was associated with a two-layered, intranuclear structure, the intranuclear element (IE). The SPB was laterally positioned on the nuclear envelope before the nucleus migrated into the well-developed sterigma. It was laterally or subapically positioned during this migration and the globular elements had greatly enlarged since interphase II. Microtubules were not clearly associated with the SPB at interphase II or early in migration to the sterigma. A mitotic division was initiated toward the apical end of the sterigma on which basidiospore development had apparently begun. The nucleus migrated into the spore at metaphase–anaphase with one of the ellipsoidal SPBs and its associated astral microtubules at the leading end of the nucleus. The nucleus contained two fibrillar nucleoli at interphase II and granular nucleoli during mitosis. The role of the SPB and IE and the implications of the results for evolution within auricularioid fungi are discussed.