Antagonistic effects of ethyl methanesulfonate and maleic hydrazide in inducing somatic mutations in the stamen hairs of Tradescantia clone BNL 4430.

Abstract

Mutagenic interaction between ethyl methanesulfonate (EMS; a monofunctional alkylating agent) and maleic hydrazide (MH; a promutagen activated into a mutagen in plants highly likely by peroxidase) was studied in the stamen hairs of Tradescantia clone BNL 4430, a blue/pink heterozygote. Since EMS has been shown to act synergistically with X rays in inducing mutations, and mutagenic synergisms have also been observed between X rays and MH by exposing to X rays before MH treatments, EMS and MH were expected to act synergistically at least by exposing to EMS before MH treatment. Three different combined treatments were conducted, i.e., by exposing for 4 h to 18.8 mM EMS 44 or 20 h before starting or 20 h after completing 1 mM MH treatments for 4 h. Unexpectedly, however, clear antagonistic effects in inducing somatic pink mutations were detected after all these combined treatments. Especially, the induced mutation frequency by exposing to EMS 44 h before the MH treatment was significantly lower than that induced by MH alone. The clear mutagenic antagonisms observed were thought to have resulted from EMS-caused inhibition of activation of MH by peroxidase, EMS ethylating and thus inactivating this enzyme or its precursors. Decreased peroxidase activities than those after treatments with MH alone were measured after two combined treatments, i.e., 12 h after the one exposing to EMS 44 h before MH and 24 h after the other exposing to EMS 20 h after MH, but the decreases were not large enough or their fluctuations were too large to judge them to be statistically significant. Comparisons of mutation frequencies induced by the combined treatments exposing to EMS before MH with those by MH alone suggest that there are some mechanisms (other than ethylation of peroxidase or its precursors) by which EMS suppresses the activation of MH.