Relative biological effectiveness of 14.1 MeV neutrons for somatic mutations induced in the diploid oat seeds presoaked in water

Seeds of a genetic stock of diploid oats (2n=14) which is heterozygous for the plant color (al/+) were presoaked for periods ranging from 0 to 48 hours and then exposed to X rays or 14.1MeV fast neutrons. The RBE of 14.1MeV fast neutrons for the reduction of seedling height was 11.5 in dry seeds, while much lower RBEs of 2.4, 1.9, 1.3 and 1.2 were obtained from 6, 12, 24 and 48 hour presoaked seeds, respectively. The RBE obtained from dry seeds for the induction of somatie mutations was 24, but the corresponding values were 4.0, 2.3, 1.9, and 1.7 in 6, 12, 24 and 48 hour presoaked seeds, respectively. Decrease of RBE values in wet seeds was thus clearly demonstrated and lower values are close to those from other organisms than to those from dry seeds of higher plants. The results show clearly that water content is one of the major modifying factors of RBE values. Other possible modifying factors were also discussed.