Population responses in tobacco cell cultures during selection for resistance to para-fluorophenylalanine

Growth of cell suspension cultures of Nicotiana tabacum L. line TX1 is strongly inhibited by concentrations of para-fluorophenylalanine (PFP) >300 μM. Through step-wise selection, lines capable of growing in 450 μM PFP can readily be obtained. The manner in which the initial resistant variant population arises, however, is not consistent with a model involving rare appearance of individual mutant cells within the population. The latter model is also not supported by the results of reconstruction experiments which show that a very substantial subpopulation of resistant cells must be present in order to allow a growth response in the presence of the selection agent.