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R A Volkov

Publications and source records attributed to R A Volkov.

7 recordsLinked to original sources
PubMed2004

Dynamic changes in the distribution of a satellite homologous to intergenic 26-18S rDNA spacer in the evolution of Nicotiana.

An approximately 135-bp sequence called the A1/A2 repeat was isolated from the transcribed region of the 26-18S rDNA intergenic spacer (IGS) of Nicotiana tomentosiformis. Fluorescence in situ hybridization (FISH) and Southern blot analysis revealed its occurrence as an independent satellite (termed an A1/A2 satellite) outside of rDNA loci in species of Nicotiana section Tomentosae. The chromosomal location, patterns of genomic dispersion, and copy numbers of its tandemly arranged units varied between the species. In more distantly related Nicotiana species the A1/A2 repeats were found only at the nucleolar organizer regions (NOR). There was a trend toward the elimination of the A1/A2 satellite in N. tabacum (tobacco), an allotetraploid with parents closely related to the diploids N. sylvestris and N. tomentosiformis. This process may have already commenced in an S(3) generation of synthetic tobacco. Cytosine residues in the IGS were significantly hypomethylated compared with the A1/A2 satellite. There was no clear separation between the IGS and satellite fractions in sequence analysis of individual clones and we found no evidence for CG suppression. Taken together the data indicate a dynamic nature of the A1/A2 repeats in Nicotiana genomes, with evidence for recurrent integration, copy number expansions, and contractions.

Base Composition↗
PubMed1999

Elimination and rearrangement of parental rDNA in the allotetraploid Nicotiana tabacum.

Origin and rearrangement of ribosomal DNA repeats in natural allotetraploid Nicotiana tabacum are described. Comparative sequence analysis of the intergenic spacer (IGS) regions of Nicotiana tomentosiformis (the paternal diploid progenitor) and Nicotiana sylvestris (the maternal diploid progenitor) showed species-specific molecular features. These markers allowed us to trace the molecular evolution of parental rDNA in the allopolyploid genome of N. tabacum; at least the majority of tobacco rDNA repeats originated from N. tomentosiformis, which endured reconstruction of subrepeated regions in the IGS. We infer that after hybridization of the parental diploid species, rDNA with a longer IGS, donated by N. tomentosiformis, dominated over the rDNA with a shorter IGS from N. sylvestris; the latter was then eliminated from the allopolyploid genome. Thus, repeated sequences in allopolyploid genomes are targets for molecular rearrangement, demonstrating the dynamic nature of allopolyploid genomes.

Base Sequence↗
PubMed1997

Structural analysis of rDNA in the genus Nicotiana.

The nucleotide sequence of the intergenic spacer (IGS) region between the 25S and the 18S rRNA coding regions has been determined for tobacco (Nicotiana tabacum). The IGS (5140 bp in length) can be subdivided into several regions (I-VII) two of which, upstream and downstream of the putative transcription initiation site (TIS), contain prominent subrepeats (A and C). The unique sequence in the central part of the IGS (region IV) preceding the TIS is extremely AT-rich. The distance from the putative TIS to the 5' end of the 18S rRNA gene is 3005 bp. The IGS sequences are compared with potato (Solanum tuberosum) and tomato (Lycopersicon esculentum) IGS. Restriction mapping of 13 Nicotiana species shows that considerable rDNA repeat length heterogeneity in this genus is probably due to different numbers of A and C subrepeats.

Base Composition↗
PubMedDate not supplied

[Effect of Cu2+ and Ni2+ on the intensity of RNA synthesis in corn seedlings].

It has been found that Cu and Ni at contents of 17 mg/kg and 64 mg/kg dry weight respectively in leaves tissues have no visible effect on morphological and physiological characteristics of plants and increase [3H]uridine incorporation in various types of RNA. Under these conditions synthesise of nuclear RNA has been found 1.8-2.4 more intense, transport RNA -2.0-2.8 intense and ribosomal RNA-1.2-2.8 intense in comparison with control. Analysing our data it is possible to suggest that the activation of the RNA synthesis under the heavy metals influence may be one of the protective mechanism connected with the plant cell adaptation to the stressful conditions.

Copper↗
PubMedDate not supplied

[Plant rDNA: organisation, evolution, and using].

Ribosomal DNA comprises a considerable part of a plant genome and is organized in tandemly arranged repeats composed of conservative coding sequences for ribosomal RNA and rapidly evolving spacer elements. We determined the nucleotide sequences of intergenic spacer regions (IGS) for five species from Solanacaea family: Solanum tuberosum, Atropa belladonna, Nicotiana tabacum, N. tomentosiformis, and N. sylvestris. The detailed comparative analysis of these and some other rDNA sequences allowed us to reveal the general regularities of evolution and functional organization of the rDNA spacer region and to clarify better phylogenetic relationships between the species within Solanacea family. A large body of experimental data on the application of rDNA in plant breeding, taxonomical studies and biotechnology are provided and discussed.

Amino Acid Motifs↗
PubMedDate not supplied

[Protein synthesis in maize haploids and diploids during cultivation under normal conditions and in the presence of phenol].

14C-leucine incorporation in cytoplasmic protein was compared for three haploid forms, three derivative autodiploid lines and four hybrid forms of maize. It has been found that the precursor incorporation in the haploid forms was by 15-20% higher that in appropriate autodiploid lines. However, the level of protein synthesis wes practically the same for all investigated diploid forms. Thus, the increase of the ploidy level correlates with the decrease of the cytoplasmic protein synthesis. It was also shown that the protein content was practically equal in haploid and diploid forms. Proceeding from the authors' data one can conclude that the protein distraction may also have different intensity. The next step of the investigation was the study of the effects of the chemical factor of cytoplasmic protein synthesis in maize seedlings with different ploidy levels in vivo. It has been revealed, that the rate of 14C-leucine incorporation in the cytoplasmic proteins differ for the haploid forms which grew on the Knop media with the addition of phenol (0.05%) and without pollutant. Nevertheless, approximately equal level of 14C-leucine incorporation was observed for autodiploids. Recently it was demonstrated that the synthetic intensity of different RNA fractions is higher in the haploid maize forms than in the diploid ones and that the haploid and diploid forms of maize display the different reaction on phenol pollution. When comparing our data with the published results it is possible to conclude that the hypothesis about the low intensity of metabolism in haploid plants, existing in literature, is not true. The authors suppose that the high activity of synthesis of nuclear, transfer and ribosomal RNA and cytoplasmic proteins in the haploid plants may be connected with high mitotic activity. The authors' data are in agreement with the hypothesis that the ratio of nuclear volume and surface determines the metabolism rate.

Diploidy↗