Chromosomal Localization of the 18S-5.8S-26S rDNA Loci in Thinopyrum ponticum (Podp.) Liu Wang and Related Diploid Species by Fluorescence In Situ Hybridization

摘要

Fluorescence in situ hybridization (FISH) was used in a decaploid species, Thinopyrum ponticum (Podp.) Liu & Wang, and its related diploid species, to investigate the distribution of the 18S-5. 8S-26S ribosomal RNA genes (rDNA) with a cloned DNA probe (pTa71). All of the three diploid species, Th. bessarabicum (Savul and Rayss) A Loeve, Th. e-longatum (Host) D. R. Dewey and Pseudoroegneria stipifolia (Czern ex Nevski) A. Loeve, have a similar distribution pattern of thel8S-5. 8S-26S rDNA. Two 18S-5.8S-26S rDNA loci were observed in each somatic cell at metaphase and interphase. One was located near the terminal end and another was on the interstitial regions of the short arms of one pair of chromosomes. However, all of the 18S-5. 8S-26S rDNA major loci in Th. ponticum were located on the terminal end of the short arms of chromosomes, and one chromosome just has one major locus. The maximum number of major loci detected in metaphase spreads of root-tip cell was twenty, which was the sum of that of their progenitors. The interstitial loci, existing in the possible diploid genome donor species have been "lost" in evolution of the decaploid species. A lot of minor loci were also detected on whole regions of two pairs of homologous chromosomes. The results indicated that the position of 18S-5. 8S-26S rDNA loci in Triticeae might be changeable rather than being fixed. The evolutionary significance of the distribution of the 18S-5.8S-26S rDNA was also discussed.