Modification of the effectiveness of fission neutrons versus 60co gamma radiation in barley seeds by oxygen and seed water content

Abstract

Conger B. V. and Carabia J. V. Modification of the effectiveness of fission neutrons versus 60 Co gamma radiation in barley seeds by oxygen and seed water content . Radiation Botany 12 , 411–420, 1972.—Himalaya barley seeds (caryopses) were adjusted to different water contents ranging from 2·2 to 32·0 per cent. Seeds ranging from 2·2 to 13·0 per cent were irradiated in vacuo with varying doses of 80 Co γ radiation or unmoderated fission neutrons and then soaked in oxygen- or nitrogen-bubbled water for ~18 hr at 0°C. Seeds ranging from 19·7 to 32·0 per cent water contents were irradiated without oxygen control at ~5°C and soaked in air-bubbled water after irradiation. The relative biological effectiveness (RBE) of fission neutrons compared to 80 Co γ radiation for seedling growth reduction varied depending on the water content of the seeds and the post-irradiation soaking atmosphere. Fission neutrons were 54–60 times more effective than y radiation in seeds 2·2 to 13·0 per cent water soaked in nitrogen-bubbled water after irradiation. For seeds soaked in oxygen-bubbled water after irradiation, fission neutrons were 7·6 times more effective than γ radiation in seeds of 2·2 per cent water content. As the seed water content was increased to 13·0 per cent the RBE increased to almost 60. As the seed water content was increased still further to 19·7, 24·5 and 32·0 per cent, the RBE decreased so that at the highest water content, fission neutrons were only 7·5 times more effective than · radiation. Nuclear volume also increased with increasing seed water but probably not enough to account for the large increase in radiosensitivity. The additional water per se , especially that in the embryo, may be the most important factor influencing radiosensitivity, especially to γ radiation.