Ref ID : 7544
Miyake Akio, Klaus Heckmann, and H.-D. Gortz; Meiosis in Blepharisma japonicum. Protistologica XV(4):473-486, 1979
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The pregamic divisions of micronuclei in conjugation of Blepharisma japonicum were investigated at 24 degrees C using new techniques. Cells before conjugation have approximately 19 micronuclei, each with a diameter of about 1.5 um. All micronuclei begin to swell 2.5 hr after the formation of heterotypic pairs. More than half of them then pass through five well-identifiable stages of prophase, including a "parachute stage" at 4.5-6 hr, and complete the first pregamic division at 12.5 hr. The rest of the nuclei remain swollen until 12 hr, and then disappear. In late prophase at 10.5 hr, about 59 chromatin bodies can be distinguished. They condense into spherules and unite to form a laurel-crown-like structure at 11 hr. The crown soon disintegrates into 59 spherules which form a metaphase plate at 11.5 hr. The nucleus then divides with a long separation spindle. After a short interkinesis, several nuclei enter prometaphase and 59 chromatin spherules appear again. These spherules are slightly smaller than those in the previous division. One of these nuclei, while still in prometaphase, migrates to a cytoplasmic region anterior to the cytostome. It then enters metaphase and divides at 15 hr producing two pronuclei. Exchanges of migratory pronuclei between conjugants and karyogamy soon follow at 16.5 hr. At the metaphase of metagamic divisions and at the metaphase of mitosis in binary fission, about 118 chromatin spherules can be counted. The peculiar unequal division without a distinct metaphase which was cliamed to occur at 4-7 hr after pairing of cells (Suzuki, 1957) was not observed by us at any time. We conclude that, at least in our material, the pregamic divisions consist of meiosis I and II. A postmeiotic pregamic division usually occuring in other ciliates is lacking. The most probable haploid number of chromosomes for B. japonicum is 59.