mutagenic effect of gamma rays on leaf protoplasts of haploid and dihaploid Nicotiana plumbaginifolia, estimated by valine resistance mutation frequencies

Leaf protoplasts isolated from haploid and dihaploid Nicotiana plumbaginifolia plantlets were treated with different doses of gamma-rays and their survival was determined by scoring for plating efficiency at each irradiation dose. A fixed number of surviving protoplast-derived colonies was then plated in the presence of inhibitory concentrations of L-valine and incubated until growing resistant calli could be scored and mutation rates calculated. Though haploid protoplasts were found to be a little more sensitive than dihaploids to the lethal effect of radiation, the two dose-response curves of gamma-rays that induced mutagenesis were very similar. The irradiation dose capable of causing a ten-fold increase of spontaneous mutation frequencies was about 500 rads with both haploid and dihaploid protoplasts.