title: Epigenetic variation of cultured somatic cells: evidence for gradual changes in the requirement for factors promoting cell division.
abstract: Cells of higher plant species in culture sometimes lose their requirement for an exogenous supply of a cell division factor that, thereafter, they are able to produce. This heritable change, known as cytokinin habituation, appears to be an epigenetic one rather than a classical mutation because it is directed, potentially reversible, leaves the cell totipotent, and involves the expression of a latent differentiated function. By using cloned cell lines derived from pith parenchyma of tobacco, we have obtained evidence that the habituation process is gradual rather than all-or-none and leads to progressively more autotrophic tissues. Cells in culture show reversible shifts among a range of habituated states but remain totipotent and can be induced to regain their requirement for a cell division factor. Thus, it appears that habituation involves epigenetic changes in a quantitative cellular phenotype. Our findings support the hypothesis that tumor progression in crown gall, a neoplastic disease of higher plants, can be accounted for by heritable changes in the pattern of gene expression.
mesh_terms: D002454:Cell Differentiation; D002455:Cell Division / Q000187:drug effects*; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D002999:Clone Cells / Q000166:cytology; D003583:Cytokinins / Q000494:pharmacology*; D010641:Phenotype; D010937:Plant Growth Regulators / Q000494:pharmacology*; D010947:Plants, Toxic; D013997:Time Factors; D014026:Nicotiana
chemical_list: D003583:Cytokinins; D010937:Plant Growth Regulators
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