XVI International Botanical Congess
In many zoosporic fungi, sporangia are formed by the delimitation of multinucleate cytoplasm from the rest of the thallus and cleavage of cytoplasm leads to the formation of zoospores. We observed that some of the nuclei were degenerated before cleavage of cytoplasm during minicycle sporogenesis of Allomyces macrogynus and Achlya spp. Nuclear degeneration was also observed during the development of sporangia of Phytophthora palmivora formed on agar. Degenerating nuclei were not observed after a fibrous plug was placed in the papilla. Ultrastructural studies suggest that the degeneration of nuclei occurs as a process of autophagy. Previous reports on nuclear degeneration in zoosporic fungi were compared with this study and the significance of the degeneration of nuclei was discussed in relation to the uniformity of zoospores.