Effect of the selective medium on the manifestation of mutations induced with mono-alkylating agents in Chlamydomonas reinhardi

The mutagenic action of methyl methanesulfonate (MMS), methyl ethanesulfonate (MES) and ethyl methanesulfonate (EMS) has been investigated in an arginine-requiring mutant (arg-I−) of Chlamydomonas reinhardi. At comparable lethality, MMS and MES were more effective than EMS in inducing the reversion of arg-I−. The frequency of mutations was greatly enhanced when the treated cells were plated on a selective medium supplemented with arginine. A more detailed study of this phenomenon was carried out after treatment with MMS. The frequency of mutations appears to depend on the concentration of arginine in the selective medium and on the number of viable cells plated on arginine-supplemented medium. These results support the view that several residual divisions are required for full manifestation of the mutations induced by mono-alkylating agents in Chlamydomonas.