Chromosome spatial arrangements on metaphase plates of intergeneric intertribal cell hybrids ofNicotiana chinensis and Atropa belladonna as well as interspecific somatic hybrid plants of Nicotiana plumbaginifolia and Nicotiana sylvestris were analyzed. In the metaphases of the first divisions of protoplast fusion products, chromosomes of the two parents were spatially separated (segmented metaphase). In long-term cultured somatic hybrids, the topology of genome separation pattern in both callus cells and plants showed changes in form from "segmental" to "radial." Growing the hybrid cells in the presence of colchicine resulted in random chromosome arrangement both in cells directly exposed to different colchicine concentrations and in colchicine-treated cells grown in colchicine-free media. The degree of genome separation calculated for different cell clones remained constant during in vitro propagation of cells but was significantly lower for subclones derived from colchicine-treated cells. Therefore, it is concluded that spatial chromosome arrangement in metaphase is epigenetically controlled.As early as 1925, chromosomes were observed to be positioned on the metaphase plate in a specific manner (1). Nevertheless, up till now the spatial arrangement of chromosomes at interphase and at mitosis and, in particular, the arrangement of the parental genomes in a hybrid cell still remained poorly understood. It is known that the arrangement and orientation of the parental (maternal and paternal) chromosomes are nonrandom in the zygote and the early stages of cleavage in some animal species (2-4). In the case of sexual hybrids between barley and rye, it was shown that the spatial separation of the parental genomes tends to persist for a large number of regular mitoses in somatic tissues (5). These facts and other information suggest that spatial separation of parental genomes in the somatic tissues of a sporophyte is of general occurrence, which has probably remained unnoticed due to the fact that in somatic cells, obtained by sexual crosses, maternal and paternal genomes are morphologically identical and, hence, difficult to distinguish. The hybridization of somatic cells permits the combination of cells of phylogenetically remote species which may have morphologically distinguishable chromosomes. Segmental disposition of the parental genomes at first metaphases after fusion (6-9) has a simple explanation and does not necessarily mean that this separation would persist through a large number of subsequent mitoses. Previous studies on the chromosome arrangement of progeny cells derived from somatic hybrids were limited almost exclusively to preparations treated with colchicine, a treatment known to result in distortion of chromosomal arrangements (7, 9-13). One early investigation (14) indicated that, within the hybrid metaphase plate of Nicotiana-Atropa somatic hybrids, the chromosomes of the two parents were unevenly distributed. This prompted a study of the chromosome arrangement in somatic cell hybrids of A...

The genetic constitution of the cell hybrids Atropa belladonna + Nicotiana chinensis, obtained by cloning of individual heteroplasmic protoplast fusion products (Gleba et al. 1982) and cultured in vitro for 12 months, has been studied. The study comprised 11 hybrid cell clones of independent origin and included analysis of a) chromosome number, size, morphology, and relative position in metaphase plates, b) multiple molecular forms of the enzymes esterase and amylase, and c) relative nuclear DNA content. The data obtained permit us to conclude that, after one year of unorganized growth in vitro, the cells of most (8) clones had retained chromosomes of both parents, while species-specific elimination of nearly all Atropa chromosomes had occurred in three clones. About half of the non-segregating clones possess 120-150 chromosomes including 50-70 of Atropa and 50-90 of Nicotiana. Other clones are polyploid and possess 200-250 chromosomes with a predominance of either Atropa or Nicotiana chromosome types. Only a few chromosomal changes (reconstituted chromosomes, ring chromosomes) have been detected. In some metaphase plates, chromosomes of the two parents tend to group separately, indicating non-random arrangement of chromosomes of the two parents within the hybrid nucleus. Cytophotometric studies of the relative nuclear DNA content showed that distribution histograms for cell clones were similar to those of non-hybrid cultured cells. Cell populations were relatively homogenous and do not indicate any genetic instability as a result of hybridization between remote plant species. Biochemical analysis of isoenzyme patterns confirmed that in most cell clones, species-specific multiple molecular forms of esterase and amylase from both parents were present, i.e. genetic material of both parental species was expressed in the cell hybrids.

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The mycelial colonies of Trichoderma viride were grown between two thin cellophane films for exact measurements. The results obtained testify to the fact that in a mature colony the average length of intercalary cells, the average number of intercalary cells in an internode and the average internode length are stable. At this stage of morphogenesis the mean internode length is shown to be equal to the product of the average intercalary cell length and the average number of intercalary cells in an internode. The coefficients of variation of the internode length and the number of intercalary cells in an internode are found to be equal. The length of an intercalary cell and duration of the doubling cycle of an apical cell of T. viride obey the law of Gamma distribution. According to our observations, the Gamma distribution is typical for the length and duration of the doubling cycle of any bacterial cells and cells of any multicellular organisms.