A LIGHT AND ELECTRON-MICROSCOPIC STUDY OF MITOSIS IN THE CLAMP CONNECTION OF AURICULARIA-AURICULA-JUDAE

Nuclear behavior and mitotic division in living and fixed somatic hyph ae of Auricularia auricula-judae were studied with phase-contrast, flu orescence, and electron microscopy to clarify the process of mitosis i n Auriculariales sensu stricto for cytological and phylogenetic analys is. Both conventional chemical fixation and freeze-substitution method s were employed for electron microscopic analysis. Mitotic division be gan when one of the two nuclei was moving into the clamp and lasted ab out 12-18 min. The spindle pole body had an electron-opaque central co re surrounded by an electron-transparent zone from prometaphase to ana phase. The spindle changed the orientation of its long axis from a pos ition 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 in tact with polar fenestrations. Nuclear division in the dikaryotic hyph a was asynchronous. The data obtained from mitosis in A. auricula-juda e support a close relationship of Auriculariales s.str. with homobasid iomycetes. The phylogenetic significance of the nuclear division chara cters is analyzed.