Document Detail

Different patterns of rDNA organization at interphase in nuclei of wheat and rye.
MedLine Citation:
PMID:  1527177     Owner:  NLM     Status:  MEDLINE    
The physical location of the rDNA repeating units (25 S, 18 S and 5.8 S rRNA genes and the intergenic spacer sequences) was investigated in rye (Secale cereale L.) and wheat (Triticum aestivum L.) root tip meristematic cells by in situ hybridization using light and electron microscopy. The rDNA sequences are organized differently in the two related and intercrossable species. In rye (2n = 14, one pair of chromosomes with nucleolar organizing regions, NORs), two condensed blocks of rDNA-containing chromatin occurred in each interphase nucleus. The blocks were associated with the periphery of nucleoli and a single-labelled, decondensed rDNA fibre extended into the nucleolus from the block. We term this expression pattern terminal decondensation. In wheat (2n = 6x = 42, five pairs of chromosomes with NORs), inactive condensed labelled chromatin was found unassociated with nucleoli. Active NORs had some condensed rDNA associated with the nucleolar periphery, but, in contrast to rye, condensed rDNA was also found within the nucleolus. The condensed labelled rDNA in wheat nucleoli was visible as fluorescent foci in the light microscope and labelled condensed chromatin in the electron microscope. Its absence in rye shows that condensed rDNA need not be present in active plant nucleoli. Diffuse labelled sites of rDNA, likely to represent actively transcribed rDNA, were found in both rye and wheat. Active rDNA loci in wheat have many expressed segments separated by unexpressed, condensed, rDNA-fragmented decondensation-while each locus in rye has a single, unexpressed perinucleolar condensed block of rRNA genes. Thus the positions of actively transcribed genes within the tandem arrays of rDNA at each locus are fundamentally different in the two cereals. The NOR chromosome appeared to extend through the nucleolus, and active rDNA sequences did not loop out from chromatin into the nucleolus as is frequently described in nucleolar models.
A R Leitch; W Mosgöller; M Shi; J S Heslop-Harrison
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Journal of cell science     Volume:  101 ( Pt 4)     ISSN:  0021-9533     ISO Abbreviation:  J. Cell. Sci.     Publication Date:  1992 Apr 
Date Detail:
Created Date:  1992-10-16     Completed Date:  1992-10-16     Revised Date:  2006-11-15    
Medline Journal Info:
Nlm Unique ID:  0052457     Medline TA:  J Cell Sci     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  751-7     Citation Subset:  IM    
Department of Cell Biology, JI Centre for Plant Science Research, Norwich, UK.
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MeSH Terms
Cell Nucleolus / metabolism
Cell Nucleus / metabolism*
DNA Probes
DNA, Ribosomal / genetics,  metabolism*
Gene Expression
Secale cereale / genetics*
Triticum / genetics*
Reg. No./Substance:
0/DNA Probes; 0/DNA, Ribosomal

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