| The RBE of 14.1 MeV fast neutrons and 137Cs
gamma rays in the pre-soaked seeds of Triticum boeoticum and its
autotetraploid Sadao ICHIKAWA Laboratory of Genetics, Faculty of Agriculture, Kyoto University, Kyoto, Japan Seeds of Triticum boeoticum BOISS. (KU 101-1), a diploid wheat species having A genome, and of its autotetraploid (KU 201-1) were soaked for 14 hours at 20C and were irradiated acutely with 14.1 MeV fast neutrons or with 137Cs gamma rays at the National Institute of Genetics, Misima. The ranges of fast neutron doses applied were 121 to 502 rads and 207 to 753 rads for the diploid and autotetraploid, respectively, and those of gamma-ray doses were 291 to 1164 rads and 437 to 1746 rads, respectively. The number of seeds employed for each dose was 30 or 60. The treated and control seeds were immediately carried back to Kyoto in a wet condition and were sown in wooden flats. Plants were grown in a greenhouse. Measurements of seedling height and dry weight were performed 31 and 49 days after irradiaion, respectively, and the effects of fast neutrons and gamma rays were compared. It was found that fast neutrons caused more growth inhibition than gamma rays. Values of the Relative Biological Effectiveness (RBE) of 14.1 MeV fast neutrons to reduce seedling height as compared with 137Cs gamma rays were calculated to be 3.12 and 2.66 for T. boeoticum and its autotetraploid, respectively. The RBE values in reducing dry weight were 3.52 and 2.74 for the diploid and autotetraploid, respectively. The RBEs in the pre-soaked seeds determined in the present study are evidently much lower than those usually obtained from higher plants with 14.1 MeV fast neutrons (ca.10 to 25), 0.43 to 4.7 MeV fast neutrons (ca. 10 to 100), or other heavy particles (ca. 10 to 50). Considering that most of the earlier high RBEs have been obtained from irradiation of dry seeds containing a small amount of water (ca. 10 to 15 percent), it seems to be reasonable to interprete that water content does modify RBE value. It is well known that gamma or X rays are less effective in causing damages in the case of irradiation of dry seeds than in the case of irradiation of wet systems such as growing plants, while the effectiveness of neutrons is changed only slightly by water content. The above interpretation that water content modifies RBE is supported by the author's recent data from Tradescantia stamen hairs (ICHIKAWA, in press). (Supported partly by the grant from the Ministry of Education, No. 96014, 1968). (Received February 16, 1970) |