A light and electron microscopic study of mitosis in the clamp connection ofAuricularia auricula-judae

Abstract

Nuclear behavior and mitotic division in living and fixed somatic hyphae of Auricularia auricula-judae were studied with phase-contrast, fluorescence, and electron microscopy to clarify the process of mitosis in Auriculariales sensu stricto for cytological and phylogenetic analysis. Both conventional chemical fixation and freeze-substitution methods were employed for electron microscopic analysis. Mitotic division began when one of the two nuclei was moving into the clamp and lasted about 12 – 18 min. The spindle pole body had an electron-opaque central core surrounded by an electron-transparent zone from prometaphase to anaphase. The spindle changed the orientation of its long axis from a position parallel to the long axis of the clamp or hypha in prometaphase, to an oblique position in early metaphase, and finally to a parallel position again in midmetaphase. The nuclear envelope was disrupted in prometaphase to early metaphase and showed discontinuity at both polar and central regions in late anaphase; however, in metaphase it was intact with polar fenestrations. Nuclear division in the dikaryotic hypha was asynchronous. The data obtained from mitosis in A. auricula-judae support a close relationship of Auriculariales s.str. with homobasidiomycetes. The phylogenetic significance of the nuclear division characters is analyzed. Key words: Auricularia auricula-judae, electron microscopy, light microscopy, mitosis, phylogeny.