45s rdna regions are chromosome fragile sites expressed as gaps in vitro on metaphase chromosomes of root-tip meristematic cells in lolium spp45 s rdna区域表示为染色体脆弱的网站差距采用体外中期染色体上的分生细胞lolium spp.pdf

45S rDNA Regions Are Chromosome Fragile Sites Expressed as Gaps In Vitro on Metaphase Chromosomes of Root-Tip Meristematic Cells in Lolium spp 1 1 1 2 1 Jing Huang , Lu Ma , Fei Yang , Shui-zhang Fei , Lijia Li * 1 Key Laboratory of Ministry of Education (MOE) for Plant Development Biology, College of Life Sciences, Wuhan University, Wuhan, China, 2 Department of Horticulture and Interdepartmental Plant Physiology and Molecular Biology, Iowa State University, Ames, Iowa, United States of America Abstract Background: In humans, chromosome fragile sites are regions that are especially prone to forming non-staining gaps, constrictions or breaks in one or both of the chromatids on metaphase chromosomes either spontaneously or following partial inhibition of DNA synthesis and have been well identified. So far, no plant chromosome fragile sites similar to those in human chromosomes have been reported. Methods and Results: During the course of cytological mapping of rDNA on ryegrass chromosomes, we found that the number of chromosomes plus chromosome fragments was often more than the expected 14 in most cells for Lolium perenne L. cv. Player by close cytological examination using a routine chromosome preparation procedure. Further fluorescent in situ hybridization (FISH) using 45S rDNA as a probe indicated that the root-tip cells having more than a 14- chromosome plus chromosome fragment count were a result of chromosome breakage or gap formation in vitro (referred to as chromosome lesions) at 45S rDNA sites, and 86% of the cells exhibited chromosome breaks or gaps and all occurred at the sites of 45S rDNA in Lolium perenne L. cv. Player, as well as in L. multiflorum Lam. cv. Top One. Chromatin depletion or decondensation occurred at variou