Tomasz Ilnicki

Tissue culture triggers chromosome alterations, amplification, and transposition of repeat sequences in Allium fistulosum.

Structural alterations in nuclei and chromosomes of cells derived from callus culture of Allium fistulosum have been studied with fluorescent in situ hybridization (FISH) using 5S ribosomal DNA (rDNA), 45S rDNA, and 375-bp repeat probes. A high frequency of chromosome abnormalities was found to be caused by the loss of telomere-located 375-bp repeats, chromosome fusion, and subsequent breakage-fusion-bridge cycles. Products of chromosome fusions and monocentric and regularly shaped chromosomes showed additional 375-bp repeat and 45S rDNA clusters at unusual sites, suggesting dynamic copy-number changes and transposition of these repeats. Southern hybridization revealed no differences in the 375-bp repeat and 45S rDNA repeat array order or the degree of methylation between DNA isolated from leaves or tissue-culture cells. In addition, protruding, spike-like structures positive for 375-bp repeats were identified on the surface of different-sized nuclei. Transmission electron microscopy analysis revealed the accumulation of densely packed chromatin within spike-like structures. Because root calyptra cells showed similar structures, it is likely that heterochromatic spike-like structures are a feature of nondividing cells at the onset of programmed cell death.

Plant biosystematics with the help of cytology and cytogenetics

The importance of cytological and cytogenetic information in the investigation of evolutionary history of species, i.e. biosystematics (cytotaxonomy) and cytogeography, is surveyed. The main issues considered are the numbers and morphology of the chromosomes, the distribution and amount of the different types of chromatin in chromosomes, nuclei at interphase stained with classical and molecular cytogenetic methods, e.g. fluorescence in situ hybridization (FISH), genomic in situ hybridization (GISH) and bacterial artificial chromosome (BAC), painting chromosomes, the isolation of large DNA segments using e.g. pulse-field gel electrophoresis, and chromosome disposition in the cell nucleus. A wide ranging biosystematic interest puts emphasis with the help of cytological and cytogenetic methods on getting to know chromosome variation within the family, genus and species connected with the phenomena of hybridization and polyploidization. Chromosome variation among taxa includes differences in the morphology and numbers of chromosomes, the amount of DNA, the sizes of chromosomes, inner chromosome structure, and DNA sequence, often shown in chromosome bands or various proportions of AT and GC pairs. On this basis we can track the course of evolution among taxa and determine reciprocal relationships. One of the main aims of our work, apart from getting to know evolutionary processes, is to create a taxonomic system of organisms.

Karyotype and nuclear DNA content of hexa-, octo-, and duodecaploid lines of Bromus subgen. Ceratochloa

The subgenus Ceratochloa of the genus Bromus includes a number of closely related allopolyploid forms or species that present a difficult taxonomic problem. The present work combines data concerning chromosome length, heterochromatin distribution and nuclear genome size of different 6x, 8x and 12x accessions in this subgenus. Special attention is paid to the karyotype structure and genomic constitution of duodecaploid plants recently found in South America. Hexaploid lineages possess six almost indistinguishable genomes and a nuclear DNA content between 12.72 pg and 15.10 pg (mean 1Cx value = 2.32 pg), whereas octoploid lineages contain the same six genomes (AABBCC) plus two that are characterized by longer chromosomes and a greater DNA content (1Cx = 4.47 pg). Two duodecaploid accessions found in South America resemble each other and apparently differ from the North American duodecaploid B. arizonicus as regards chromosome size and nuclear DNA content (40.00 and 40.50 pg vs. 27.59 pg). These observations suggest that the South American duodecaploids represent a separate evolutionary lineage of the B. subgenus Ceratochloa, unrecognized heretofore.