[Physical mapping of the 45S rDNA and 5S rDNA to rice prometaphase chromosome]

Rice (Oryza sativa L.) is one of the most important cereal crops in the world. The chromosomes of rice are relatively small in size. With the help of fluorescence in situ hybridization (FISH), several rice DNAs have been localized on rice chromosomes. 45S rDNA and 5S rDNA are encoding sequences for ribosomal RNA synthesis. For detecting the chromosomes related to 45S rDNA and 5S rDNA, the digoxigenin-dUTP labeled probe DNA was probed to the prometaphase chromosomes which were prepared from the root tips harvested from an indica rice variety, Zhongxian 3037. For identification of the chromosomes, slides were stained with Giemsa before FISH. With the improved FISH protocol 45S rDNA was clearly detected on two pairs of chromosomes which are usually found to be attached to nucleolus. The signal size between two pairs of the chromosomes was different. According to the characteristics of the chromosomes, the chromosomes with bigger signal were chromosome 9 and the other pair were chromosome 10. They were also discriminated from arm ratio. The signals of 5S rDNA were relatively small but clear. According to the size and arm ratio of the chromosome with FISH signals, the 5S rDNA was mapped on the short arm of chromosome 11, very close to the centromere region.