RADIATION EFFECTS ON <i>ARABIDOPSIS THALIANA</i>. I

Abstract

RBE values of fission and 14MeV neutrons with respect to γ-rays in Arabidopsis were studied by specific locus method. F2 seeds from the cross between the single recessive hairless mutant and the wild hairy strain (race Landsberg) were used in this experiment, because of the difficulty to obtain many F1 seeds.Dry seeds were subjected to 1.2, 2.1 and 2.9krad of fission neutrons and to 0.8, 1.9, 2.6 and 4.4krad of 14MeV neutrons. 23.6 to 47.3krad of γ-irradiations were also carried out in each neutron experiment. Experiments were carried out under continuous light in an air-conditioned room. Around 90 per cent of seeds germinated in the controls and in all γ-ray and neutron lots. Almost all seedlings survived.During the growth of seedlings, segregation ratio of hairless homozygotes was examined. They segregated according to the ratio of 3:1 in all lots. Therefore, hairy plants must have consisted of 1/3 dominant homo- and 2/3 heterozygotes.Should somatic mutation from dominant hairy to recessive hairless occur in heterozygotic seeds, it would appear on some part of the plant body. Some of hairy plants in the irradiated lot had some leaves or parts of leaf without hairs. The frequency of plants with hairless sectors increased with increasing dosage both in γ-ray and neutron lots. A non-linear relation taking rather the shape of an exponential curve, was observed for the γ-ray group, whereas the frequency versus neutron dosage was nearer to linear relationship. Hence RBE of neutrons depends on dosage or frequency. The very rough estimate of the RBE for somatic mutation at 1 per cent frequency is about 15 and 16 for 14MeV and fission neutrons, respectively. The possibility that the mutation is caused by chromosomal aberrations is disccussed.