Analysis apaptosis phenomena of nuclei in zygospores of Phycomyces

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Phycomyces is multinucleate and thousands of nuclei transfer from parental gametangia into zygospores when two mating types were mated. Only one or two diploid nuclei, however, are able to survive until the end of the dormancy period of about 6 months. The other remained nuclei lose their functions and gradually disappear with an increase in the age of zygospores. To explore the mechanisms of this apaptosis phenomenon of nuclei, the zygospores were inspected for the age-dependent changes of their characteristics.1. The zygospores increased in their physical hardness after the 10th day of the mating, about 5 times harder than the zygospores before 10 days after mating. The hardness recovered to the normal just before the zygospore germination. Emergence of a large central oil-drop is another characteristic of the post-10th-day zygospores. The oil drop also disappeared before the germination.2. Genetic analyses of nuclei in the spores developed on sporangiophores and hyphae which regener … More ated from the incised zygospores with different ages revealed that meiosis has not completed before 10th day after mating. No regeneration of any structures occurred on the post-10th day zygospores.3. The zygospores formed between the heterokaryotic parents with several different genetic markers were selected and their protoplasm including nuclei were transferred into the sporangiophore segments of an auxotropic mutant. The spore analysis for recombination of genetic markers of the regenerants on the sporangiophore segments implied that meiosis occurred in the zygospores around 30th day after the mating.4. Microscopic and electromicroscopic observations revealed that the nuclei increased in their volumes at the 7-8th days after mating but sharply decreased after the 10th day till the 20th day.5. Aggregation of some degenerated nuclei was found in the aged zygospores after the 30th day. Nuclei with broken membrane were also found. These findings imply that all the nuclei except for the survive diploid nucleus(ei) lose their functions 10 days after mating. Less