Ultrastructural Studies of Nuclear Division in Basidiobolus Ranarum Eidam

SUMMARY

Electron microscopy shows that nuclear division in the parasitic phycomycete Basidiobolus ranarum, is mitotic despite some atypical features. The nuclear envelope partially fragments in prophase but regains much of its integrity, except at the equator, by metaphase. The spindle axis forms along the long axis of the hypha in prometaphase, is normal to the hyphal axis in metaphase, and again lies along the hyphal axis in anaphase. Chromatin is not identifiable until prometaphase when at least 900 minute chromosomes appear. Each chromosome has a pair of conical kinetochores, each of which is associated with a single spindle microtubule (chromosomal fiber). Anaphase movement is effected by both chromosome movement towards the poles and separation of the poles. Single, very short, perinuclear centrioles migrate to the poles in early prophase and replicate by metaphase. The nucleolus disperses in prophase, but the granular component collects in the polar regions during metaphase and anaphase. These granules aggregate in telophase reforming the nucleoli without apparent association with specific chromosomal loci.