Chloroplast Mutagenesis: Effect of N-Methyl-N′-Nitro-N-Nitrosoguanidine and Some Other Agents on Euglena

Treatment of normal green Euglena gracilis with N-methyl-N'-nitro-N-nitrosoguanidine results in permanent loss of the ability to form chloroplasts in close to 100 percent of the organisms. The resulting "bleached" strains can be maintained for over 100 generations; no reversion to chloroplast-containing organisms occurs within this time. Alkylating agents, azaserine, mitomycin C, acridines, nitrous acid, hydroxylamine, and gamma-irradiation do not bleach significant proportions of cells even at concentrations sufficient to kill most of the cells. These results may be due partly to differences in the base compositions of nuclear and chloroplast DNA.