| Summary: | 碩士 === 國立臺灣大學 === 植物學研究所 === 84 === The nucleolar organizer regions ( NORs ) of five Nicotiana species belonging to section Alatae were investigated by conventional cytological technique, fluorescence in situ hybridization ( FISH ) and silver staining. For FISH, clone pRY18 carrying a 3.8 kb 17S-5.8S-25S repeat of rice ribosomal DNA ( rDNA ) was labeled with digoxigenin- 11-dUTP and used as a probe to hybridize chromosomal DNA in root- tip cells. The results showed that : (1) two pairs of chromosomes in N. alata (2n=18),N. longiflora (2n=20) and N. plumbaginifolia (2n =20), and three pairs of chromosomes in N. langsdorffii (2n=18) and N. sylvestris (2n=24) possessed rDNA loci ; (2) in N. alata and N. sylvestris the sizes of NORs in one pair of chromosomes were polymorphic. In all species, the number of chromosomes with secondary constrictions determined by Feulgen staining corresponded to the number of AgNORs revealed by silver staining. Comparison of the results from FISH with those of obtained by Feulgen and silver staining indicated that in N. langsdorffii and N. plumbaginifolia rDNA one pair of chromosomes was not functioning.
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