Synergistic effect of combined treatments of gamma radiation and ethyl methanesulfonate in barley

In these experiments 3H-labelled ethyl methanesulfonate (EMS) was used to study the effect of gamma rays on the uptake of EMS by barley seeds and the resultant alkylation of macro-molecules. In a parallel experiment the combined effect of gamma rays and EMS on mutation frequency and efficiency was investigated. Gamma irradiation (10, 20 and 30 kR) inhibited the uptake of [3H]-EMS, resulting in fewer alkylations in the macromolecular fraction. In the combined treatments with unlabelled EMS, seedling injury as well as frequency of mitotic and meiotic chromosomal aberrations were less than additive. However, a synergistic effect of combined treatment was observed for the induction of chlorophyll mutations in the M2 generation. The results rule out the increased uptake of the chemical mutagen as the cause of the observed synergism, and suggest the interaction of radiation- and chemically-induced lesions