Ethyl methanesulfonate-induced chloroplast mutagenesis in crops

Ethyl methanesulfonate (EMS) was used to induce “chlorophyl chimeras” in a number of crop species (peas, carrots, soybeans, lentlls, and radishes). One percent EMS was optimal for mutation treatment in all species tested. In an ultrastructural study of the carrot “mutants” with sorting-out variegation several photobleaching “mutants” with enlarged magnograna and photostable “mutants” with reduced grana stacking were observed, similar to plastome mutants observed in other species. A unique “mutant” with normal grana stacks but no stroma Iamellae was obtained. None of the carrot “mutants” was transmitted to the M2 generation because of embryonic lethality of the “mutant” tissue. Photobleaching mutants outnumbered photostable mutants 2:1. In the pea chimeras some mutants were transmitted to the M2; a virescent mutant with a slower development of internal membranes and a mottled mutant with extremely underdeveloped plastids were noted. These data suggest that EMS will be a useful mutagen in many species where chlorophyll mutations are required for physiological or genetic work.