21. The third 45S rDNA locus in 0. eichingeri (CC) newly detected by an improved FISH method R. shishido, y. sano and K. Fukui

1) Plant Breeding Institute, Faculty of Agriculture, Hokkaido University, Sapporo 060, Japan

2) Hokuriku Natl. Agr. Exp. Stn., Joetsu 943-01, Japan

 The variability of 45S rDNA in Oryza species has been analyzed by Fukui et al. (1994). It gives us useful information to understand organization and characterization of rice genome structure. We also characterized 0. eichingeri (CC, 2n = 24) genome by using a fluorescence in situ hybridization (FISH) method with 45S rDNA as the probe. The FISH method for localizing DNA sequenses on chromosomes by using fluorochrome is now well known as the effective method. Furthermore, the remarkable improvement Fig 1. Fluorescence in situ hybridization of 45S rDNA in 0. eichingeri. a. Counter-stained nucleus with DAPI. b. Fluorescent signals of 45S rDNA in nucleus. c. Counter-stained chromosomes with DAPI. d. Fluorescent signals of 45S rDNA on chromosomes.
Research Notes 85
in high sensitivity of a cooled CCD camera and image analyzing systems make it possible to detect the positions of the probe even on small rice chromosomes in spite of the weak fluorescent signals.

Fukui et al. (1994) have already reported the two 45 S rDNA loci in 0. eichingeri. Applying the improved method of FISH, we succeeded in detection of the additional 45 S rDNA locus in 0. eichingeri (Fig. 1). Fluorescent signal of the third 45S rDNA locus newly found was extremely small and weak. It is not easy to detect the locus constantly as compared with other two loci (Table 1). In addition to the detection of the new 45S rDNA locus, we defined the chromosome numbers with the 45S rDNA locus as chromosome 4, 9 and 11. The loci on chromosome 4 and 9 have been localized at the distal end of the short arms, and the locus on chromosome 11 has been localized at the proximal region of the short arm. Concerning the intensity of the signals, the locus of chromosome 4 was the strongest among three loci and the locus of chromosome 11 was the weakest. Fukui et al. (1994) and Shishido et al. (1994) reported that another deploid C genome species, 0. officinalis has also three 45S rDNA loci. Thus it is concluded that the diploid C genome species have three loci for 45S rDNA on chromosome 4, 9 and 11.

Table 1. Frequency of the fluorescent signals of 45S rDNA in 0. eichingeri


Chromosome 4 Chromosome 9 Chromosome 11 Number of cells observed
12 12 6 6

References

Fukui, K., N. Ohmido and G.S. Khush, 1994. Variability in rDNA loci in the genus Oryza detected through

fluorescence in situ hybridization. Theor Appl Genet 87: 893-899. Shishido, R., T. Kinoshita, N. Ohmido and K. Fukui, 1994. Analysis and utility of chromosome information 68. The third rice 45S rDNA locus locates on the chromosome 11. Breed. Sci. 44 (2): 2.