Valery G. Grif

Bio: Valery G. Grif is an academic researcher from Russian Academy of Sciences. The author has contributed to research in topics: Heterochromatin & Euchromatin. The author has an hindex of 2, co-authored 2 publications receiving 33 citations.

Some aspects of plant karyology and karyosystematics.

Abstract: The significance of the 4C value (where C is the amount of DNA in the unreplicated haploid genome) in angiosperm plants is discussed. The DNA amount is a stable feature used in biosystematics. Although this parameter varies even in closely related taxa, there is no correlation between the DNA amount and the structural and functional organization of plants. The role of DNA amount, including "excess" DNA, in plant evolution is considered. Some rules governing the distribution of DNA amount among different plant taxa are postulated, together with the possibility of using the data in systematics, phylogeny, and solutions of problems of genetic apparatus organization and evolution. The decrease in DNA value per genome during plant evolution and the high level of species formation in taxa with large DNA values have been shown. Plant taxa with a small DNA value per genome have a high percentage and higher degree of polyploidy. The nature of the differential staining of euchromatin and heterochromatin bands of prophase and metaphase chromosomes is also discussed. Data that could explain the mechanism of heterochromatin visualization under cold pretreatment of cells are reviewed. Phenomena involved in the arrangement of chromocenters in interphase nuclei and chromosomes in metaphase during consecutive cell generations are discussed.

Intrapopulation and individual polymorphism of heterochromatin segments in Trillium camschatcense Ker.-Gawl.

Abstract: SUMMARYThe present work reports the study of the topography and the size of the heterochromatin segments (H-segments) in the chromosomes of the plant of Trillium camschatcense Ker.-Gawl. from a Kamchatka population with the help, of a special chromosome analysis, computer program. The staining techniques used are C- banding and fluorochroming with Hoechst 33258. A high level of hereditary polymorphism as well as somatic chromosome aberrations appearing de novo has been found. The heterochromatin of Trillium camschatcense appears to be of a polymorphic labile system creating a wide variation spectrum within the population. It is postulated that it could be the onset of divergences into separate forms and the subsequent creation of new species.

The Incidence of Polyploidy in Natural Plant Populations: Major Patterns and Evolutionary Processes

Abstract: Polyploidy, the multiplication of chromosome sets above the diploid state, is arguably as prevalent in plants as any other eukaryotic group. Over the past century, polyploidy has been linked with particular taxonomic groups (flowering plants, ferns), northern latitudes and extreme environments, and life histories such as perenniality, asexuality and self-fertilization. Here we review the current state of evidence for these patterns and their interpretations. Our understanding of the incidence of polyploidy in plants is still in flux due to a progression of advances in cytogenetics, flow cytometry, phylogenetics and genomics. We find polyploidy to be highly heterogeneous among plant groups and estimates of intraspecific variation and hybrid forms are increasing with high throughput analyses. Surprisingly, many accepted trends between polyploidy and geography, mating system, and comparative rates of species diversification have become less strong or conflicting with the development of new procedures, in particular with phylogenetic approaches. Our review suggests that while some patterns remain strong, many are not universal, suggesting there may be no unified explanation for the success of polyploids in plants.

Genome Size and the Phenotype

Abstract: Land plant species (Embryophyta) vary more than 2,300-fold in the size of the holoploid genome (C-value) (see Leitch and Leitch 2012a, this volume) with the extremes at both ends of the scale contributed by angiosperms. At the lower end we find some species of the carnivorous Lentibulariaceae with ultrasmall genomes, e.g. Genlisea aurea with 0.065 pg or 63.5 Mbp (1C) (Greilhuber et al. 2006). This is only about 0.40-fold the size of the genome of Arabidopsis thaliana with 0.16 pg or 156.5 Mbp (1C) (Bennett et al. 2003), a species long considered to be the plant with the smallest reliably determined genome size. At the upper end of the scale stands the monocot octoploid Paris japonica (Melanthiaceae) with 2n = 8x = 40 and 152.23 pg or 148.88 Gbp (1C) (Pellicer et al. 2010). Nevertheless, other monocot species such as Fritillaria davisii (69.45 pg, 1C; 2n = 2x = 24, a possible palaeotetraploid), Trillium apetalon (95.0 pg, 1C; 2n = 4x = 20), and the dicot tree parasite Viscum album (102.9 pg, 1C; 2n = 20, palaeotetraploid?) also rank high on the scale regarding monoploid genome size (i.e. Cx-value = 2C-value divided by ploidy level) (Zonneveld 2010). From these examples it is clear that polyploidy plays only a relatively small role in the origin of the huge genome size differences reported. Instead, it is the accumulation of retroposon-like and other repetitive elements in the genomes which are largely responsible for the huge diversity of genome sizes in plants (Bennetzen et al. 2005; Grover and Wendel 2010; see also Kejnovsky et al. 2012 in Volume 1). (N.B. Recent studies using flow cytometry to estimate genome size in species with enormous genomes have highlighted how the more traditional approach of estimation using Feulgen densitometry may considerably underestimate genome size at this upper end of the scale (Zonneveld 2010).)

Independently Regulated Neocentromere Activity of Two Classes of Tandem Repeat Arrays

Abstract: Tandem repeat arrays often are found in interstitial (i.e., normally gene-rich) regions on chromosomes. In maize, genes on abnormal chromosome 10 induce the tandem repeats that make up knobs to move poleward on the meiotic spindle. This so-called neocentromere activity results in the preferential recovery, or meiotic drive, of the knobs in progeny. Here we show that two classes of repeats differ in their capacity to form neocentromeres and that their motility is controlled in trans by at least two repeat-specific activators. Microtubule dynamics appear to contribute little to the movement of neocentromeres (they are active in the presence of taxol), suggesting that the mechanism of motility involves microtubule-based motors. These data suggest that maize knob repeats and their binding proteins have coevolved to ensure their preferential recovery in progeny. Neocentromere-mediated drive provides a plausible mechanism for the evolution and maintenance of repeat arrays that occur in interstitial positions.

The distribution of B chromosomes across species

Abstract: In this review we look at the broad picture of how B chromosomes are distributed across a wide range of species. We review recent studies of the factors associated with the presence of Bs across speci