Nucleolar organizer activity in wheat, rye and derivatives analyzed by a silver-staining procedure

Karyotype characterization of Crotalaria juncea (L.) by chromosome banding and physical mapping of 18S-5.8S-26S and 5S rRNA gene sites

“…Silver staining techniques have been used to detect transcriptional activity at NORs, assuming that silver binds to NOR-associated proteins that are part of the transcriptional machinery (Guillén et al, 2004). Thus, the expression of rDNA has been assessed by the silver staining method, and inactive loci have been found in several groups of plants, particularly in hybrids and allopolyploids such as Triticum species and several types of wheat-rye derivatives (Cermeño et al, 1984;Neves et al, 1997).…”

Activity of rRNA Genes from Rye Chromosome in Translocation Mutant forms of T. Aestivum L

“…Analysis of nucleolar activity in triticale cultivars (4,5,16,17,22) confi rm the complete suppression of expression of rye origin rDNA in triticale as a result of nucleolar dominance and genomic interactions in AABBRR cultivars.…”

Chromosomal localization of ribosomal DNA sequences in an apple rootstock using a digoxygenin detection system

“…[23]. Secondary constrictions which have been associated with plant NORs in some studies [4,5,10,16,24] were not observed． Hybridization of the rDNA sequence was detected at a 90％ frequency(over ten preparations) as patches of dark purplish-brown precipitate at the end of the short arms of chromosomes 6 and 14 (Fig 1b)，while control preparations(either DNase pretreatment of chromosomes or hybridization without a probe) failed to give such a colour reaction． Nucleolar organiser regions stained with silver were visible as tight black spots whereas non-specific staining was yellowish brown and tended to be more diffuse． The ten preparations examined indicated the presence of NORs at a frequency of 70％ for chromosome 6 and 90％for chromosome 14．NORs were present at the end of the short arms for both chromosome pairs． These results confirm the localization of ribosomal R N A genes detected with in situ hybridisation by the rDNA probe (Fig 2) since the acidic silver staining of ribonucleic protein accumulating around active NORs in interphase and remaining at mitosis is an indication of gene activity at rDNA sites during the preceding interphase [14]． When silver stained interphase preparations were screened to determine the maximum number of nucleoli and hence number of active rDNA loci，most interphase nuclei were found to contain one large nucleolus formed by complete fusion of nucleoli during the cell cycle，but few contained two, three, or the primary number of four [25], indicating that all four rDNA loci can be active as reported for AraNdopsis [13]. The nucleoli were of two size classes (Fig 3), reflecting differences in amount or rate of transcription at the rDNA loci on chromosome pairs 6 and 14, or difierent rates of assembly or export of ribosomes [ 26]． Onr finding that rDNA genes in Malus are localized on two pairs of chromosomes is consistent with earlier in situ hybridization for the diploid angiosperm species including A11ium cepa，A．fistulogum, AraNdopsis thaliana，Pisum sativum ，and Hordeum vulgare.…”

“…There are two recent reports on karyotype analysis for Arabidopsis which has chromosomes of comparable size but fewer in number (2n=10) than Malus (2n=34) [12,13]. This group used digoxygenin labelling coupled with a fluorescent detection system to determine the chromosomal localization of rDNA (9kb probel and of a smaller tandem repeat sequence(380bp probe)．Although there is a recent report[8l of successful in situ hybridization to chromosomes of a woody gymnosperm (Picea)，there are no such reports for woody angiosperms． This paper describes the use of digoxygenin-labelled apple rDNA sequences(18S coding sequence plus spacer)as a probe along with an enzyme一1inked colour reaction to hybridize to MM106 chromosomes．The position of the nucleolar organiser regions，the site of ribosomal RNA transcription [14,15] was determined by silver staining to provide independent verification of the rDNA probe results．The number of active ribosomal gene loci can also be confirmed by counting nucleoli (sites of ribosome biogenesis)in interphase nuclei [13,14,[16][17][18]]．…”