Karyotype analysis of Nicotiana kawakamii Y. Ohashi using DAPI banding andrDNA FISH

Prometaphase cells were used to analyze the karyotype of Nicotiana: kawakam ii Y. Ohashi by means of sequential Giemsa/CMA/DAPI staining and multicolor fluorescence in situ hybridization with 5S and 18S rDNA. Observation of th e DAPI-stained prometaphase spreads indicated that N. kawakamii had six pai rs of large chromosomes, one pair of medium-sized chromosomes and five pair s of small chromosomes. The six pairs of large chromosomes possessed remark able DAPI bands, and each could be identified from both the DAPI banding pa ttern and the length of the short arm. The DAPI banding pattern was approxi mately identical to the CMA and Giemsa banding patterns. Hybridization sign als of the 18S rDNA probe were detected on two pairs of large chromosomes. In addition, two pairs of small chromosomes were identified based on the po sition of the 5S rDNA signals. An idiogram of N. kawakamii chromosomes was produced based on DAPI bands and rDNA loci.