Abnormal spore cleavage: Abnormal spores of Allomyces macrogynus

In the aquatic phycomycete Allomyces macrogynus abnormal spore cleavage takes place in the presence of colchicine or benomyl resulting in multinucleate–multiflagellate spores due to failure in the formation of cytoplasmic microtubules after the induction of zoosporogenesis. The 27 cytoplasmic microtubules which normally surround the nucleus and nuclear cap of the mature spore are not formed in the presence of colchicine or benomyl. At high concentrations of colchicine (4–8 mg/ml) the spores do not have a flagellum. Colchicine or benomyl inhibit microtubule formation during zoosporogenesis and also appear to perturb the mobilization of the gamma bodies which are believed to be the source of the vesicles which form the axonemal membrane and cleavage furrows. These observations are discussed in relation to the hypothesis of Heath that cytoplasmic microtubules formed during zoosporogenesis determine cytoplasmic domains which will delimit the spore initials at cleavage. The observations presented here appear to confirm this hypothesis.