Fig. 6. Simultaneous visualization of chromatin (DAPI staining in blue) and rDNA hybridization sites (red) in meristematic interphase nuclei of rye, showing the major patterns of rDNA organization. (a) Type I: condensed perinucleolar knobs (arrows) without any traces of labelled rDNA chromatin inside the nucleolus. (b) Type II: condensed perinucleolar knobs (arrows) with thin filaments of rDNA chromatin towards the interior of the nucleolus (bracket). (c) Type III: condensed perinucleolar knobs (arrows) with intranucleolar condensed rDNA spots (arrowheads) linked by thin chromatin filaments (hybrid rye line). Bar, 5 µm. Note that rDNA perinucleolar knobs are usually present on the nuclear hemisphere where DAPI staining is more intense, indicating a higher concentration of chromatin in this pole of the nucleus.

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