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Advisor(s)
Abstract(s)
Summary. The nucleolar organizer regions (NORs) are composed of
hundreds of rRNA genes, typically spanning several megabases. Cytologically,
NORs include regions that are highly condensed and regions
that are decondensed, the latter corresponding to regions at which associated
proteins stain intensively with silver (Ag-NORs) and where active
rRNA gene transcription is thought to occur. To test the relationship between
rRNA gene activity, NOR silver staining, and rDNA (genes
coding for rRNA) chromatin condensation, we used the DNA methyltransferase
inhibitor 5-azacytidine to evaluate the correlation between
the epigenetic regulation of rRNA genes and NOR silver staining in the
plant Secale cereale. Following 5-azacytidine treatment, we observed an
increase in rRNA gene transcription as well as a reduction in the number
of cells showing a significant difference in the size of the silver-stained
domains in the two NORs. These transcriptional changes occurred concomitantly
with an increase in nuclear and nucleolar size and were associated
with the reallocation of most of the rDNA from perinucleolar
heterochromatin into the nucleolus. Collectively, these results suggest
that rRNA gene transcription, silver staining, and NOR decondensation
are interrelated in S. cereale.
Description
Keywords
nucleolar organizer region transcription silver staining 5-Azacytidine Secale cereale