Aberrant Chromosome Movement and Spindle Formation in Meiosis of Bromus Hybrids: An Interpretation of Spindle Organization

Walters, Marta Sherman

doi:10.2307/2439260

Cited by 18 publications

(15 citation statements)

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“…Similar behavior of single chromosomes or small groups of chromosomes has been observed by a number of workers, including Clark (1940) in a study of the effect of a recessive gene on spindle formation in Zea and Walters (1958) in a study of meiotic behavior in three Bromus hybrids. The observations in these various plants indicate that spindle formation with few exceptions is associated with isolated chromosome groups down to the level of single chromosomes, and that spindle size is related to the number of chromosomes involved.…”

Section: Discussionsupporting

confidence: 79%

“…The occurrence of multiple spindles or of spindles with multiple poles or with non-convergent poles has been re garded as evidence for the existence of such entities as "pole determinants" (Darlington andThomas 1937, Swanson andNelson 1942) or "spindle or ganizers" (Walters 1958). In the present material, single chromosomes or small groups of chromosomes that were not included in the restitution nuclei were commonly observed to be associated with spindle development and often undergoing the post-restitution division (Figs.…”

Section: Discussionmentioning

confidence: 57%

“…The occurrence of high univalent frequencies, restitution nuclei, and such abnormalities as cell cleavage that is out of phase with chromosome behavior has also been reported at microsporogenesis in many wide hybrids. Walters (1958), for example, observed these irregularities, along with others, in a study of three intersectional hybrids in Bromus. In a consideration of the pre restitution chromosome behavior in her material, Walters arrived at an inter pretation that is basically similar to that applied to the present Paspalum material.…”

Section: Discussionmentioning

confidence: 60%

“…As Walters (1958) has indicated, the type of complex pre-restitutional chromosome movement described above poses certain problems for an hy pothesis of metaphase orientation of the chromosomes and their subsequent anaphase behavior such as that proposed by Ostergren (1951). According to the mechanistic concept of Ostergren, the orientation of kinetic granules, of which there is one per chromosome, determines the intact pole-ward movement or equatorial positioning of univalent chromosomes.…”

Section: Discussionmentioning

confidence: 99%

“…8-10). Many cells at this stage resemble a usual first anaphase and have been regarded as such by Walters (1958).…”

Section: Discussionmentioning

confidence: 99%

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Asyndesis and Meiotic Non-reduction in Microsporogenesis of Apomictic <i>Paspalum secans</i>

Snyder

1961

CYTOLOGIA

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An earlier paper (Snyder 1957) was concerned with the occurrence of obligate apomixis in several clones of Paspalum secans Hitchc. and Chase collected in the vicinity of Mayaguez, Puerto Rico, the type locality of the species.The clones investigated were found to be aposporic, with embryo development initiated by autonomous diploid parthenogenesis.Normal develop ment of the embryos and the formation of caryopses, however, were found to depend on fertilization of the polar nuclei and subsequent endosperm forma tion, i.e., the clones studied are pseudogamous.Meiotic behavior during megasporogenesis was not studied in detail, although large numbers of uni valent chromosomes were readily apparent at diakinesis and first metaphase. The primary megasporocytes commonly degenerate without dividing, but when meiosis does occur it was found to consist of two divisions resulting in the formation of a triad or tetrad of non-functional megaspores.A preliminary consideration of microsporogenesis in a number of clones revealed almost complete asyndesis at diakinesis and first metaphase, and the predominant production of dyads of microspores.The present study has been concerned with the details of meiotic behavior during microsporogenesis in several clones of the species. The nature and extent of the irregularities in meiosis are of interest in view of the pseudogamous characteristic of the materials, and also in relation to certain theories concerning mechanisms involved in the meiotic process.

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Section: Discussionsupporting

confidence: 79%

Section: Discussionmentioning

confidence: 57%

Section: Discussionmentioning

confidence: 60%

Section: Discussionmentioning

confidence: 99%

“…8-10). Many cells at this stage resemble a usual first anaphase and have been regarded as such by Walters (1958).…”

Section: Discussionmentioning

confidence: 99%

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Asyndesis and Meiotic Non-reduction in Microsporogenesis of Apomictic <i>Paspalum secans</i>

Snyder

1961

CYTOLOGIA

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Multipolar Meiosis in Diploid Crested Wheatgrass, Agropyron Cristatum

Tai¹

1970

American J of Botany

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A new model of spindle organizers is proposed: The spindle organizer in a higher plant is similar to the centriole of animal cells. It is a unit cell organelle which follows regular cell division cycles and is genome specific. Each genome carries its own spindle organizer. During fertilization, a male spindle organizer enters the egg cell. It may fuse with the female spindle organizer, or either one may degenerate. In a hybrid, both male and female spindle organizers may exist, and multipolar divisions separate different genomes into different groups. The same mechanism can be used to explain the formation of a polyhaploid from a polyploid. The chromosome behavior of an individual is believed to be an interaction of chromosome homology and the homology between chromosomes and their spindle organizers. This model is based on observations of multipolar meiosis which occurred in two cultures of diploid crested wheatgrass, Agropyron cristatum (L.) Gaertn. In these two cultures multipolar meiosis occurred at every stage after late diakinesis. The seven bivalents were separated into groups at late diakinesis. More than one equatorial plate was formed at metaphase I. Each micrometaphase plate behaved as an independent unit and had its own anaphase movement. Usually the chromosome complement separated into two groups with (4–3), (5–2), and (6–1) separations observed in about an equal number of cells. Cells with chromosomes divided into three or four groups were found less frequently. Multipolar meiosis may take place at either first or second division. Cell plates were formed across each spindle apparatus, cleaving each group of chromosomes into smaller micro‐cells. At the “quartet” stage, 4‐ to 12‐celled “quartets” were observed. Pollen stainability was measured at above 75% in both cultures. Stained pollen grains could be classified into two distinct size classes. Darkly stained, small pollen grains represented the result of multipolar meiosis and may have been viable. Multipolar cell divisions provided a mechanism which polyploids might reduce their ploidy level.

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