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A long-term callus culture from Luzula luzuloides leaf meristem subcultured for over one year was examined cytologically. In the control material most of the mitotic cells (95.97%) represented diploid level and standard chromosomes in terms of length (2n = 12AL). Aneuploidy occurred with low frequency (4.03%), with somatic chromosome numbers 2n = 13, 14 resulting from partial agmatoploidy. Karyotype analysis of control material showed differences in chromosome length ranging from 4.94 µm to 3.19 µm in prometaphase, 3.54 µm to 2.54 µm in mid metaphase, and 2.81 µm to 1.88 µm in late metaphase. Callus cells exhibited a wide range of chromosome number variation (2n = 7-48), although a high percentage of cells (61.39%) represented the standard karyotype (2n = 12AL). Variability in chromosome number and karyotype structure was a consequence of chromosome fission (partial and total agmatoploidy), chromosome fusion (partial symploidy) as well as aneusomaty and polyploidy. There was no evident correlation between the frequency of structural and numerical chromosome variation and the duration of callus culture. The cells with modified karyotype appeared in particular collections.
The organization of spindle microtubules (MTs) was examined by light microscopy in mitotic cells of Luzula luzuloides, a plant with holokinetic chromosomes. Allium cepa cells were used as comparative material. Spindle structure and mitotic chromosomes were studied using phase-contrast microscopy and confocal laser scanning microscopy (CLSM) following anti-α-tubulin labeling and propidium iodide staining. The mitotic chromosomes of Luzula were rod-shaped and approximately similar in length, and did not possess primary constrictions. Luzula chromosomes untreated with saturated solution of α-bromonaphthalene, aligned in the metaphase plate, could not be observed as individuals. Their anaphase movement was specific; the spindle attachment was not localized but evenly distributed along the poleward edge of the chromosomes so that the chromatids moved apart in parallel, not forming the classical V-shaped figures characteristic of monokinetic chromosomes. The spindle of Luzula was relatively short with distinct blunt poleward ends. Microtubules were equally spread through the metaphase plate, indicating the holokinetic nature of Luzula chromosomes.
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