The Effect of Cycloheximide on the Sporophyte of Allomyces Arbuscula

Abstract

SUMMARY When the sporophyte of Allomyces arbuscula was grown on agar containing a concentration of cycloheximide that partially inhibited growth, orange-colored reproductive structures developed on portions of the sporophyte. A few zoospores (mitospores), when allowed to germinate in the presence of cycloheximide, gave rise to plants having the appearance of a gametophyte. The antibiotics endomycin, streptomycin, streptothricin, and neomycin were either ineffective or much less effective than cycloheximide in inducing the formation of orange-colored structures. The swimming spores discharged by the paired colored and colorless structures correspond in behavior and size to male and female gametes. It is concluded that the colored reproductive structures and associated colorless structures are male and female gametangia whose formation on the sporophyte is induced by the action of cycloheximide. When sporophytic hyphae bearing male and female gametangia are isolated, they may give rise to colonies which at first display a mixture of sporophytic and gametophytic characteristics and which subsequently become either completely gametophytic or sporophytic in appearance. As a possible explanation of this behavior it is suggested that the isolated hypha from which the colony was derived contained a mixture of haploid and diploid nuclei and in time one kind became dominant over the other. Such an explanation assumes that chromosome number determines “sporophyticness” or “gametophyticness.”