Spatial separation of parental genomes in hybrids of somatic plant cells.

Chromosome spatial arrangements on metaphase plates of intergeneric intertribal cell hybrids of Nicotiana 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.