Influence of ploidy on plastome mutagenesis in Nicotiana

A clear influence of ploidy was observed on the frequency of both spontaneous and nitroso-methylurea (NMU) induced, streptomycin-resistant, adventitious shoots developing on leaf explants of Nicotiana tabacum and N. plumbaginifolia. At nearly all NMU levels employed a significantly higher yield of resistant shoots was obtained from haploid compared with diploid leaf strips. At 1 mM NMU the differences were not significant and were absent when a high (1000 mg/l) selective concentration of streptomycin sulphate was used. The influence of ploidy is discussed in relation to the possible effect of plastome copy number on mutagenesis and sorting out of resistant plastids.