ADAPTIVE RESPONSE IN THE GENE MUTATION TE ST UPON CHEMICAL MUTAGENESIS IN BARLEY

The possibility of forming an adaptive response to the mutagenic actio n of alkylating mutagen methyl nitrosourea (MNU) was studied in barley varieties Miina and Otra after treating them with low doses of MNU, t he other alkylating mutagen, nitroso-nitro-methyl guanidine (NNMG), an d a nonspecific agent, potassium cyanate, which is likely to have no e ffect on DNA at all. Pretreatment of seeds with all three of these age nts may decrease the frequency of chlorophyll mutations appearing afte r subsequent treatment with shock doses of MNU; in addition, the proba bility of forming an adaptive response depends on the interaction of t he variety genotype with the conditions of plant vegetation. Formation of an adaptive response in seeds that were treated with calcium cyana te makes the [repair{ mechanism of its development dubious. We suppose that the adaptive response in barley occurs on the basis of more univ ersal inducible processes, such as the process of stimulated repopulat ion.