Ref ID : 7677
Sergei O. Skarlato; Electron Microscope Study of the Micronuclei of the Ciliate Stentor coeruleus during Meiosis. Protistologica XVIII(3):281-288, 1982
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Conjugation in Stentor coeruleus lasts 25-30 hr and during 16-18 hr most micronuclei undergo the first two maturation divisions which are meiotic. In 30 min after pairing the moniliform macronucleus becomes fragmented into single beads. At the same time the micronuclei enter the prophase of the 1st meiotic division. They greatly enlarge and their chromosomes decondense. At the stage corresponding apparently to the leptotene of classical meiosis, the micronuclear chromatin is represented by a network of threads about 8-10 nm in diameter. Spherical bodies of fibrillar structure, 0.6-0.9 µm in diameter, develop during late leptotene among the chromatin threads. At zygotene-pachytene stages, which probably correspond to the "parachute stage", the chromosomal material condenses and synaptinemal complexes appear. The spherical bodies are still present and their diameters increase to 1.2-1.4 µm. Sometimes a direct contact between chromosomes and spherical fibrillar bodies is observed. At diplotene and diakinesis, the bivalents lose their synaptinemal complexes; the spherical bodies disappear. The metaphase of the 1st maturation division occurs after 12-14 hr of mating. The nuclear envelope remains intact throughout the 1st meiotic division, as well as in the 2nd and the 3rd ones. However, at telophase the nuclear envelopes around the daughter nuclei are re-formed by fusion of vesicles which are pinched off the old nuclear envelope inside the nucleus. The 2nd meiotic division begins shortly after the 1st one. At this stage, a number of degenerating micronuclei appear in the cytoplasm. Only one of the products of the 2nd maturation division enters the 3rd one.