ABSTRACT
Regeneration of whole plants from an isolated cell or protoplast in an ever-increasing number of species has introduced the possibility of employing these experimental systems for induction and selection of variant cell lines or mutants and, ultimately, the development of new plants for human welfare. Cell and protoplast cultures comprise an ideal system for the development of mutants. A plant cell geneticist can screen millions of cells in a small flask or dish using 104 to 105 cells or protoplasts per milliliter. Each cell or protoplast is a potential plant. Variants in tissue culture are selected on the basis of unusual phenotype. The conversion of tobacco cells to cytokinin autonomy is a gradual, progressive process which, unlike mutation, is strongly influenced by the physiological and developmental stage of cells. In earlier literature, one frequently finds instances of cell variation and the variant plants raised from them.
