Use of haploid plants as bioassay for mutagens

Results of a pilot program show that suspension cultured polyhaploid Nicotiana tabacum cells can be used to bioassay the effects of mutagens. Reproducible survival curves with significant regression coefficients are obtained. Putative mutation conferring resistance to amino acid analogs is significantly more frequent after exposure to mutagens; in contrast, habituants, cytokinin-independent clones, are significantly less frequent (although the variance of clone size increases!). The maximum spontaneous mutation rate is estimated at 3 X 10(-8); the equilibrium frequency of habituant cells in an otherwise nonhabituated culture is estimated at 5 X 10(-7). An evaluation of the system suggests changes in several and further characterization of other of the parameters involved. The use of haploid tobacco as an in vivo mutagen screen is briefly described, as is the importance of similar in vivo diploid systems for discriminating between various kinds of mutational processes.