Physical mapping of 45S rRNA gene loci in the cucumber (Cucumis sativus L.) using fluorescence in situ hybridization

The fluorescence in situ hybridization (FISH) using two different rDNA prob es (18S and 45S) mas applied to cucumber (Cucumis sativus L.) chromosomes. After counterstaining with 4'-6-diamidino-2-phenylindole (DAPI), all chromo somes showed visible bands similar to C-banding pattern and could be identi fied. The 18S and 45S rDNA signals appeared at the pericentromeric regions of chromosomes 1, 2 and 5. After silver staining to identify the nucleolar organizer region (NOR), the mitotic cells had two to four dots in nucleoli at interphase, two bands at the pericentromeric regions of two larger chrom osomes at mid-metaphase. Although no NOR-bands appeared dearly at the prome taphase stage, certain silver-stained chromosomes mere identified. DAPI sta ining made it possible to identify the silver-stained chromosomes at mid-me taphase and suggested that chromosome 1 or 2 had a silver-stained band at m id-metaphase.