[Mutagenesis and plant phylogenesis].

There are two types of genetic mutations - nuclear and cytoplasmic. We consider genic, chromosomic and genomic nuclear mutations in several seed plant families characterized by different evolutionary age and life forms. "Atlas of chromosome numbers of flowering plants" published in our laboratory in 1969 and containing information about 35 000 species and periodical "Index to plant chromosome numbers" (USA) covering in all about 150 000 species were used for comparative study of chromosome numbers. Gymnosperms originated approximately 300 000 000 years ago and represented predominantly by arboreous and shrub forms are characterized by practically total lack of polyploidy and rare aneuploidy, thus the evolutionary progress in this group has been provided by genic mutations. The morphology of chromosomes in Gymnosperms is much more uniform as compared with Angiosperms - all 200 species of Conifers have 24 large meta- and submetacentric chromosomes Angiosperms. This group originated twice later includes 300 000 species with wide range of living forms - from initial arboreous to ephemeric ones. Therefore, the dominating type of mutations for some groups of Angiosperms as Fagaceae, Aceraceae, Aquifoliaceae, Caricaceae and Lauraceae is genic one. The major part of arboreous Angiosperms has clear polyploid series like 2n = 28, 56, 84 (Betula) and 2n = 38, 76, 114 (Magnolia). Polyploidy is the prevalent type of mutagenesis because of the advantage consisting in amplification of total number of genes against a background of preservation of the genome integrity. The chromosomic type of mutations prevalent in groups with asexual reproduction provides the flow of genes between genomes as a result of aneuploidy. Genomic mutations are observed mostly in herbaceous plants. In such groups as Poaceae, Cyperaceae, Ranunculaceae and Rosaceae we observe up to 90 % of polyploid species. Due to such ploidy restrictions like the size of karyon, and the size and the number of chromosomes numerous shorter polyploid series are observed in this group. Hence primitive mutations are prevalent in ancient Gymnosperms. Chromosomic and genomic mutations arose later providing gene flow without functional changes of source genomes.

[Chromosome maps of trilliaceae: II. A study of the genome composition in polyploid species of the genus Trillium by fluorescence nucleotide base-specific staining of heterochromatic chromosome regions]. / Karty khromosom rastenii semeistva Trilliaceae (II): izuchenie genomnogo sostava poliploidnykh vidov roda Trillium pri pomoshchi fluorestsentnogo nukleotid-spetsificheskogo okrashivaniia geterokhromatinovykh raionov khromosom.

Chromosome banding with nucleotide base-specific fluorochromes chromomycin A3 (CMA) and Hoechst 33258 (H33258) was used to study the karyotypes and to construct cytological maps for diploid Trillium camschatcense (2n = 10), tetraploid T. tschonoskii (2n = 20), hexaploid T. rhombifolium (2n = 30), and a triploid T. camschatcense x T. tschonoskii hybrid (T. x hagae, 2n = 15). With H33258, species- and genome-specific patterns with numerous AT-rich heterochromatin bands were obtained for each of the four forms; CMA revealed a few small, mostly telomeric GC-rich bands. In T. tschonoskii, the two subgenomes were similar to each other and differed from the T. camschatcense genome; on this evidence, the species was considered to be a segmental allotetraploid. In T. x hagae, one T. camschatcense and both T. tschonoskii subgenomes were identified. The subgenomes of T. rhombifolium only partly corresponded to the T. camschatcense and T. tschonoskii genomes, in contrast to the morphologically identical Japanese species T. hagae. This was assumed to indicate that allohexaploids T. rhombifolium and T. hagae originated independently at different times; i.e., their origin is polyphyletic. Based on the chromosome maps, a new nomenclature was proposed for the Trillium genomes examined: K1K1 for T. camschatcense, T1T1T2T2 for T. tschonoskii, T1T1T2T2 for T. x hagae, and K1RK1RT1RT1RT2RT2R for T. rhombifolium.

Cell cycle and its parameters in flowering plants.

Data on the duration of cell cycle and its phases in meristems are reviewed for 170 species from 93 genera of 38 families of higher plants. The reviewed cell cycle parameters are submitted in tabulated form, including taxonomic and anatomical characteristics of particular subjects, methods, experimental conditions, duration of cell cycle and its phases, and references. The influence of environmental factors on the cell cycle and temperature dependence of cell cycle parameters are considered in addition to certain features and causes of daily dynamics of mitotic index. Special attention is paid to the problem of comparability of different results of determination of cell cycle duration. As shown below, the only correct comparison of cell cycle parameters in different species is that, which is based on the evidence provided at species-specific optimum temperatures. A rather simple method for determining the optimum temperature of cell division and growth is based on the analysis of root growth rate. Critical temperature points are defined to serve for determination of optimum temperature for the cell cycle. As shown below, retardation of growth rate at low temperatures results from the proportional increase in the duration of cell cycle phases, while at the minimum temperature the morphological characteristics of meristem remain unchanged. Cell division anomalies or morphogenesis disruption that occur as cell cycle parameters change may be due presumably to the shock temperature action within the tolerant limits. Our experiments have suggested that the rhythm of illumination may exert essential influence on the parameters, structure and stationarity of the cell cycle.

[Nucleotide composition of the cold-sensitive heterochromatin regions of Paris hainanensis Merrill chromosomes]. / Nukleotidnyi sostav chuvstvitel'nykh k kholodovomu vozdeistviiu geterokhromatinovykh raionov khromosom u Paris hainanensis Merrill.

Cold-induced decondensation of heterochromatic regions (CSR-bands) in Paris hainanensis (= Daiswa hainanensis Merrill Takht.) (2n = 10; 10 + b) was studied. The comparison of CSR-banding patterns with those obtained by nucleotide-specific staining with fluorochromes DAPI and chromomycin A3 demonstrated that low temperatures induced decondensation only of large AT-rich heterochromatic regions. It is suggested that this is characteristic of all plant species.

Some aspects of plant karyology and karyosystematics.

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.