Journal
CROP SCIENCE
Volume 54, Issue 2, Pages 617-625Publisher
CROP SCIENCE SOC AMER
DOI: 10.2135/cropsci2013.05.0325
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Funding
- National Council for Scientific and Technological Development - CNPq
- Foundation for Research Support of the State of Minas Gerais - FAPEMIG
- Coordination of Improvement of Higher Education Personnel - CAPES
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The distribution, number, and location of ribosome DNA (rDNA) regions on chromosomes were evaluated, and transcriptional activity was described in genotypes of Italian ryegrass (Lolium multiflorum Lam.), as well as in an offspring resulting from interbreeding. Nucleoli and nucleolar organizer regions were labeled with silver nitrate and fluorescent in situ hybridization (FISH) was performed with 5S and 45S rDNA as probes. Hybridization procedures were performed on slides previously stained with the Ag-NOR method. The 5S rDNA sites were highly conserved, while 45S rDNA sites had wide variability, even showing more than one site on the same chromosome. One of the genotypes had more than expected 45S rDNA sites. Approximately 95% of the cells at metaphases had at least one chromosome break/gap in the 45S rDNA site, resulting in chromosome fragmentation. Thus, 45S rDNA correspond to fragile sites in L. multiflorum. These events can affect genome organization and cause new chromosomal rearrangements which, along with some other factors, might be responsible for microevolutionary changes involved in differentiation and speciation. Not all 45S rDNA sites are transcriptionally active. Variation in both the number and size of nucleoli and mechanisms of nucleolar fusion were observed in L. multiflorum.
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