engleski

Size variation and peculiar behaviour of nucleolar organizer region in Quercus species

Considerable intercellular and interindividual variability of the nucleolar organizing regions (NORs) in the karyotypes of Q. petraea, Q. robur, Q. pubescens and Q. coccifera were noticed. This variability concerned size variation and rarely number variation of NORs in the karyotypes of different individuals of the same species. In general, Quercus species contain one pair of satellite chromosomes (SAT-chromosomes) bearing NORs on the terminal position. In the karyotypes of some individuals NORs were frequently detached from nucleolar chromosomes and appeared as free spherical bright yellow fragments in the cells after chromomycin A3 (CMA) staining. Because of this behaviour we had suspected them as "B-chromosomes" in our previous report. On the other hand, fragments never occurred free in meiosis and two CMA-positive dots were always located on the terminal site of the two chromosomes forming a bivalent. As the spherical fragments have been found in all investigated Quercus populations, they could not be the consequence of environmental influence. In situ hybridisation revealed hybridisation signals of 18S RNA probe on the two SAT-chromosomes or fragments, respectively, proving its role as nucleolar organizers. Present investigation carry out NOR size variation and frequency of detached NORs in comparison with NORs located on SAT-chromosomes in different individuals of the same species.

Quercus sp.; nucleolar organizing region (NOR); fluorescent staining; FISH

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