Correlation between EMS uptake by barley embryos under different treatment conditions and mutation frequency

Abstract

Uptake of ethyl methanesulphonate and its alkylation in the TCA-insoluble fraction of embryo cell lysates was followed after hull-less barley seeds (karyopses) had been treated with ³H-labelled EMS. The effects of modifying factors such as pre-soaking of seeds in water before mutagen treatment, post-soaking and drying back after treatment were investigated. The effects of the same factors on M₁ parameters and chlorophyll mutation frequencies in the M₂ were studied in parallel experiments with "cold" EMS. The uptake of EMS on the dry matter basis was greater in the embryo than in the rest of the karyopses. Movement of the mutagen or its hydrolytic products into the embryo from seed endosperm was noted during germination. Enhanced mutation frequencies in M₂, when pre-soaked seeds were treated, was partly due to greater uptake of mutagen. The mutagen and its hydrolytic products were leached out of the treated seeds during the post-soaking. This leaching out decreased the effect on M1 parameters but had no significant effect on mutation frequencies in the M₂. Drying of seeds after treatment with the mutagen and storage for seven days increased alkylation in the TCA-insoluble fraction and enhanced mutagenic and also the deleterious effects. It is concluded that at least some of th differences in mutation frequencies after various treatment procedures were due to variation in the actual dose of the mutagen ultimately received by the target cells.