Studies on combined effects of gamma radiation and N-nitroso-N-methylurethane in Pisum sativum and Hordeum vulgare

Dried pea and barley seeds were exposed to a single acute gamma-ray dose of 10 or 15 krad and 7.5 or 15 krad, respectively. Shortly after irradiation, the seeds were treated with buffered N-nitroso-N-methylurethane (NMU) solution: for peas, at 0.001% concentration over 10 hours; and for barley, at 0.01% or 0.025% over 4 hours. Under the conditions of the study, exposure to NMU solely produced no apparent effect on plant survival; in contrast, radiation alone - particularly at the higher doses - was found to considerably reduce the percentage of surviving plants. Postradiation treatment with the lethal effect and the proportion of MU diminished both sterile pea plants and, respectively, sterile barley blossoms. With combined exposures to both mutagens, additivity and superadditivity effects were seen, depending on dose levels of either agent as well as on the sequential order of exposures