ROONEY, L., and P. B. MOENS. 1973. Nuclear divisions at meiosis in the ascomycetous yeast Wickerfiarnia juoresceris. Can. J. Microbiol. 19: 1383-1387. In cultures of cells which have been on sporulation medium for 22 h, all stages of meiosis and sporulation occur. In electron microscopy of glutaraldehyde-fixed cells, spindles and spindle-pole bodies are preserved but chromosomes and kinetochores are not apparent. Photographic records of complete serial sections of some 40 asci in different developmental stages show that during the first meiotic division, the nuclear envelope remains intact and the spindle elongates from about 1 pm to 4 pm. Each of the spindle-pole bodies then divides and the bilobed nucleus contains two short spindles (one in each lobe). During the second division the spindles elongate from about 0.5 pm to 3.5 pm while the nuclear envelope remains intact. As a result there is a four-lobed nucleus, either in a chain formation or in a more compact arrangement. The spindle-pole bodies increase in complexity to varying degrees during the second division. One becomes the organizer of a complete ascospore wall while the other three may develop an inco~nplete wall and eventually these three nuclei degenerate in the cytoplasm of the ascus. It is shown that the nuclear behavior during meiosis parallels that of the yeast Sacchar.or7zyces cermisiae but differs from that reported for Euascomycetes. ROONEY, L., et P. B. MOENS. 1973. Nuclear divisions at meiosis in the ascomycetous yeast Wicker.harnia juorescens. Can. J. Microbiol. 19: 1383-1387. Dans des cultures de cellules qui ont sejournk 22 h dans un milieu a sporulation, on retrouve tous les stades de la mti'ose et de la sporulation. Lors de I'examen au microscope Clectronique des cellules fixees a la glutaraldehyde, les fuseaux et les corps polaires fusiformes sont intacts, mais les chromosomes et les cinttochores sont inapparents. L'observation photographique de toute une skrie de coupes de 40 asques prises a divers stades du developpement fait voir que, pendant la premiere division mti'otique, I'enveloppe nucleaire demeure intacte et le fuseau s'allonge de 1 pm a 4 pm. Chacun des corps polaires fusiformes se divise et le noyau bilobe contient deux courts fuseaux (un dans chaque lobe). Pendant la seconde division, les fuseaux s'allongent de 0.5 p n~ 2 3.5 11n1 tandis que I'enveloppe nucleaire demeure intacte.Comme resultat, on retrouve un noyau a quatre lobes en chainette ou en amas plus compact. Pendant la seconde division, les corps polaires deviennent plus complexes a divers degres. Un noyau devient I'initiateur d'une paroi complete de I'ascospore tandis que les trois autres peuvent causer un developpement d'une paroi incon~plete; eventuellement ces trois noyaux digenerent dans le cytoplasme de l'asque. I1 est demontre que le comportenlent nucliaire lors de la mti'ose va de pair avec celui de Snccharomyces cerevisiae mais diffkre de ce qui est rapport6 pour les Euascomycetes.[Traduit par le journal]
Photographic records of complete serial sections of asci in different stages of sporulation show that one of the four nuclear lobes produced during meiosis in the ascus of the yeast Wickerhamia fluorescens has a complex spindle-pole body, which is the site from where the presumptive ascospore wall, or prospore wall, develops and eventually surrounds the ascospore nucleus and associated cytoplasm. The three remaining nuclei develop spindle-pole bodies and prospore walls to lesser and varying degrees. With few exceptions, all three degenerate. The outer membrane of the prospore wall forms a fold, or rim, on the outside of the spore. Thickening of the spore wall takes place first in the asymmetric ring, then around the spore body, and finally at the site where the nucleus is associated with the wall. It is shown that ascospore delimitation in W. fluorescens and Saccharomyces cerevisiae are similar to each other, and that it differs from the type observed in a number of Euascomycetes.
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