engleski

Molecular cytogenetics of genus Quercus; fluorochrome banding, physical mapping of ribosomal genes and activity of NORs

The important tree genus Quercus has been intensively studied at morphological, physiological and molecular level, but little is known about its chromosomes. This is mostly attributed to the small-sized chromosomes of the decreasing row and the difficulties in getting good spreads. The latter problem was overcome by use of air-drying technique which provided sufficiently good protoplast preparations for FISH. Double-target FISH yielded good physical markers for chromosomal identification. Moreover, chromosomal distribution and loci number of genes coding for 18S-26S and 5S rRNA were established when applied simultaneous FISH. In situ hybridisation and fluorochrome banding patterns revealed identical karyotypes for eleven oak species indicating theit conserved chromosomal organisation. Two 18S-26S rDNA loci were associated with NORs and third minos 18S-26S locus was co-located with the only 5S rDAN locus on the chromosome pair possessing no secondary constriction. Sequeintial flurochrome banding showed CMA and DAPI positive bands at the juxtaposition near the centromeres of all chromosomes. However, the majority of GC differentiated heterochromatin was associated with NORs. Major 18S-26S locus positioned terminally on the only subtelocentric pair showed prominent intra- and interspecific size polymorphism. Difference in the size of hybridisation signal perfectly corresponded to CMA-signal size variation indicating that ribosomal genes are interspersed over entire heterochromatic satellites. Silver staining revealed that ribosomal genes of each cluster were transcribed preferentially in different cells and can be active independently of their location in the SC.

Quercus; molecular cytogenetics; fluorochrome banding

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