engleski

FISH mapping of 18S-5.8S-26S rRNA genes and fluorochrome banding in the triploid viviparous onion, Allium x cornutum Clementi ex Visiani, 1842

Triploid viviparous onions (Allium x cornutum Clementi ex Visiani 1842., syn Allium cepa L. var. viviparum Metzg. (ALEF.), auct.), (2n = 3x = 24), are known in some countries only as a rare relic crops, while in other parts of the world they are still traditionally or even commercially cultivated. Previous cytogenetical studies of Croatian triploid viviparous onion Ljutika, based on Giemsa C-banding, chromosome pairing analysis during meiosis, as well as genomic in situ hybridization, indicated a complex hybrid and highly heterozygous karyotype structure, with possible triparental genome organization. In this study we continued with analysis of the karyotype structure of Ljutika. Staining with fluorochromes CMA3 (Chromomycin A3) and DAPI (4, 6-diamidino-2-phenylindole) confirmed previous results of Giemsa C-banding and revealed GC rich heterochromatic regions mainly associated with chromosome ends and NORs, and only a few interstitial bands. FISH mapping of the ribosomal 18S–5.8S–26S genes revealed two major rDNA signals on short arms of two subtelocentric satellite chromosomes in almost all metaphase plates of Ljutika. The largest subtelocentric chromosome lacked rDNA signal. Significantly smaller rDNA signal was occasionally located on one small submetacentric chromosome. These results are in agreement with previously published results of nucleolus organizing regions (NORs) identification by silver-staining technique, which confirmed maximum of three nucleoli in interphase nuclei. Molecular mechanisms underlying rearrangements and activity of ribosomal genes in triploid karyotype are discussed.

Allium; triploid viviparous onions; hybrids; karyotype; fluorescent in situ hybridization; 18S–5.8S–26S genes; fluorochrome banding

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