Abstract
<p>The morphology of cell nuclei in callus obtained from root-tip meristems of <em>Allium fistulosum</em> L. (Monocotyledoneae, Alliaceae) was analysed. The most interesting phenomena observed in long-term callus culture were the different mechanisms of cell polyploidization, enlargement of telomeric segments of heterochromatin, and extensive chromatin elimination, associated with instability of nuclei size and DNA content.</p><p>Protruding heterochromatin "spikes" were observed on the surface of some di- and polyploid nuclei. The presence of these spikes was connected with the formation of small heterochromatic micronuclei frequently found in the cytoplasm. It is suggested that these micronuclei are produced by direct elimination of heterochromatin from the interphase nuclei.</p><p>Polyploid cells accumulated with each successive cell collection. The ploidy level attained by highly polyploid cells was 15C-220C. The shape of the nuclei and heterochromatin distribution suggest that polyploid nuclei in <em>A. fistulosum</em> tissue culture are produced by endoreduplication and by restitution cycles.</p>
Highlights
Genetic alterations in calli can be examined in many ways
The material was rinsed a few times in distilled water, hydrolyzed in 1N HCl at 60°C for 11 min, and stained in pararosaniline according to the Feulgen method (FM)
In the initial Allium fistulosum cultures, all the cell nuclei were similar in shape and size to the nuclei of the meristem
Summary
Genetic alterations in calli can be examined in many ways. Changes in chromosome number and nuclear DNA amount are analysed more often than abnormalities in the structure of chromosomes and interphase nuclei. Cytophotometry, densitometry and chromosome counting have generally revealed increased production of polyploid and aneuploid cells in cultured plant tissues. In some long-cultured calli almost all of the diploid cells are eliminated and replaced by polyploid cells (Bayliss 1980; Golczyk 1994). It has been suggested, that in some plant cultures opposite mechanisms operate, which decrease chromosome number and cell ploidy level (Nuti Ronchi 1991; Madej and Kuta 2001). In callus of monosomatic plant, Crepis capillaris the chromosomal stability is limited to about one year of culture and polyploid cells appear successively (Maluszynska 1997)
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