Female gamete germination and partial development in Allomyces macrogynus

Abstract

Sensitivity to activation of germination and growth was studied using unfertilized female gametes and zygotes of Allomyces macrogynus. When placed in nutrient medium, female gametes formed a branched rhizoid and a single, unbranched hypha that never formed reproductive structures during the 48-hr period of the experiment. Although partial female development was very asynchronous when compared to zygote development, nuclear divisions occurred and the nuclear cycle time was similar to that in zygote-derived hyphae over the first 7 hours of growth. After this time few divisions occurred in the female-derived hyphal nuclei. Comparison of nuclear number versus hyphal length in female- and zygote-derived hyphae showed no statistical difference, demonstrating that the actual number of nuclei was not the reason for incomplete development from female gametes. Female gametes and zygotes did not germinate in cycloheximide nor form a hyphal germ tube in actinomycin D. Motile zygotes plated on nonnutrient agar, or induced in nutrient medium before inoculation into nonnutrient liquid medium, developed a single, unbranched hypha with a small sporangium at the apical end. Ultracytochemistry with diaminobenzidine showed the presence of catalase-containing microbodies often in association with lipid bodies in female gametes. This suggested that although lipid may supply energy for female partial development, since zygotes completed development on nonnutrient medium, endogenous energy reserves are not the cause of incomplete female development.