Variation of Satellites and Localization of rRNA Genes in Peony Chromosomes.

Abstract

Summary All 4 peony plants examined, Paeonia japonica Miyabe and Takeda, P obovata Maxim., P lactiflora Pall. cv. kumoinotsuru (Higo-peony), and P lectiflora Pall. medical peony, had a diploid chromosome number of 2n=2x= 10. Their karyotypes, also, were very similar or the same and were constituted from 2 sets of chromosomes A to E. Nevertheless, the SAT-chromosome, hybridization signal of rRNA genes in interphase nuclei, and number of nucleolus per cell varied among individuals and plants. The signals of rRNA genes in metaphase localized at the distal ends of homologous chromosomes A, B, D and E (8 signals) in P japonica and 2 kinds of P lactiflora, and at the distal ends of homologous chromosomes B, D and E (6 signals) in P obovata. In conclusion, it is considered that variations in the number of satellites, signals of rRNA genes in interphase nuclei and nucleoli per cell can be attributed to the grade of interaction of rRNA genes.Two peony plants (Ranunculaceae), Paeonia japonica Miyabe and Takeda and P obovata Maxim., are growing in Japan (Ohwi 1978, Kitamura andMurata 1986). They have a chromosome number of 2n=2x=10 and a very similar or the same karyotype (Sinoto 1938, Kurita 1965, Tsutsumi and Inoue 1977, Okada and Tamura 1979, Nakamura and Nomoto 1981, 1982, Nishikawa 1985, Nakata and Hong 1991. The 5 chromosomes constituting a genomic set in the genus Paeonia have been designated as A, B, C, D and E in descending order of length (Sinoto 1938). Despite of this circumstance, the appearance of satellites on the chromosomes A to E has varied widely among previous reports (op. cit.). The SAT-chromosomes, specific chromosomes with a satellite, are associated with nucleolar organizing regions (NOR's), which are the sites of rRNA genes (Ritossa and Spiegelman 1965, Wallace and Birnsteil 1966, Phillips et al. 1971, 1974, Ramirez and Sinclair 1975, Doerschung et al. 1976, Givens and Phillips 1976. The present paper deals with the variation of SAT-chromosomes and the number of nucleoli per cell, and the chromosomal localization of rRNA genes using a in situ hybridization method in 2 wild and 2 cultivated plants. Materials and methods Material plantsTwo wild and 2 cultivated peony plants, Paeonia japonica Miyabe and Takeda, P obovata Maxim., P lactiflora Pall. cv. kumoinotsuru (Higo-peony), and P lactiflora Pall. medical peony, were used in this study. The former 2 species were collected from natural populations of Kumamoto Prefecture, i.e., Gokanosyo of Yatsushiro-gun and Takamori-machi of Aso-gun, respectively. The P lactiflora plants were cultivated in the Experimental Garden of Faculty of Science, Kumamoto University.Corresponding author. 212Akinori Uchino and Minako Miyagawa Cytologia