Effects of modifying factors on the response of rice seeds to gamma-rays and fission neutrons

Abstract

Experiments were conducted with Oryza saliva L. cv. ‘Bluebonnet’ to determine the effects of modifying factors on seed response to gamma-rays and fission neutrons. Dose rate did not affect the seed response to gamma-rays when storage-oxygen effects were minimized. Seed sensitivity to gamma-rays increased as water content was either decreased from 12–13 per cent to approximately 3 per cent or increased to approximately 20 per cent. D 50 for seeds with 2·7 per cent water irradiated in vacuo was 4·77 or 59·09 krad when seeds were soaked under oxic or anoxic conditions, respectively; OER was 12·4. Although a major role of seed water content is to mediate the extent of the oxygen effect, our results suggest also that the increase in water content from 2·7 to 13 per cent afforded a degree of protection which is oxygen independent. Storage effects were observed during as well as after irradiation in seeds with less than 13 per cent water when the oxygen effect was not eliminated. In contrast, increasing the water content from 3·8 to 16·3 per cent had little or no effect on seed sensitivity to fission neutrons; however, seeds containing 20 per cent water exhibited relatively higher sensitivity. The increase in damage at 20·3 per cent water content was probably caused by the increase in dose from the hydrogen and an increase in metabolic and physiologic activity. D 50 for seeds at 2·7 per cent water irradiated with fission neutrons in vacuo was 1·9 or 2·7 krad when soaked under oxic or anoxic conditions, respectively; OER was 1·44. There was no conclusive evidence of a storage effect following neutron irradiation of Bluebonnet rice seed. The RBE for fission neutrons based on seedling growth reduction was 2·5 or 21·9 for seeds with 2·7 per cent water soaked under oxic or anoxic conditions, respectively.