|Williams, Norman - RETIRED ARS, FARGO, ND|
Submitted to: Chromosome Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 29, 2000
Publication Date: July 1, 2001
Interpretive Summary: In the cell divisions that form reproductive cells, the number of chromosomes normally is reduced to one-half the number in other plant tissue. Plants with a heritable form for abnormal cell division are useful for studying cell division, and are also useful because they produce reproductive cells having twice the normal number of chromosomes. Our objective was to study a mutant of durum wheat that has abnormal cell division. We wanted to describe the characteristics of the mutant, to learn what caused the unusual chromosome numbers in the mutant, and to test the effects of environment on expression of the mutant trait. Examination of cells of the roots revealed that some cells had twice, or four times, the normal number of chromosomes. We also observed cells with two or more nuclei, instead of only one. Some cells had only partially completed formation of the new cell wall. These observations are consistent with a failure of cell wall formation as one cause for the abnormal cell division. However, other cells had very large nuclei, and fusion of nuclei in cells with more than one nucleus could have formed the large nuclei. As temperature increased, the rate of abnormal cell division increased. Fusion of nuclei was influenced by light, but not as much as by temperature. Three percent of mutant/durum hybrids had 42 chromosomes, instead of the expected 28 chromosomes. Therefore, unreduced reproductive cells formed in the mutant at a frequency of 3%. The unreduced reproductive cells may allow for incorporation of genetic material from related or wild species, and may speed up the process of incorporating genes from wild species.
Technical Abstract: An ethyl methanesulfonate induced, mitotic mutant of durum wheat (Triticum turgidum L. var. durum; 2n=4x=28) was found. Our objectives were to characterize the mutant, to determine the mechanism of abnormal cell division, and to test for environmental effects on abnormal cell division. Stained root-tip meristems and pollen mother cells were studied with brightfield, phase contrast, and immunofluorescence microscopy. Abnormal mitotic cells included metaphase cells with a multiple of the normal complement (8x=56, or 16x=112), multinucleate cells, 4C, 8C, or 16C uninucleate cells, and cells exhibiting incomplete cytokinesis. The mutant had three classes of pollen mother cells, euploid with normal bivalent pairing, multiploid with bivalent pairing, and multiploid with multivalent pairing. Preprophase bands and spindles were normal in mononucleate cells. Some cells had asymmetrical phragmoplast formation and dismantling that produced incomplete cytokinesis. Failure of cytokinesis and nuclear fusion were the mechanism of abnormal cell division. Seedlings were germinated in light or dark at one of four temperatures. As germination temperature increased, the frequency of abnormal cells increased. Light had a small influence on abnormal cell division. When the mutant was crossed as female with durum wheat, three percent of hybrids were hexaploid, indicating that functional-unreduced gametes had formed in megaspores.