Seed Radiosensitivity: Wide Range in Oxygen-enhancement Ratio after Gamma-irradiation of Eight Species

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Abstract
The objective of this study was to determine the oxygen effect after 60Co γ-radiation of dry seeds from eight species of higher plants which differed in radiosensitivity and nuclear and chromosome volume. Seeds of barley, rice, cucumber, fescue, lettuce, alfalfa, radish and onion were dried to a water content of between 1 and 3 per cent by storage over CaSO4 under vacuum. The seeds in vacuo in glass tubes were then exposed to 60Co γ-radiation. After irradiation, the seeds were soaked in either oxygen- or nitrogen-bubbled water at 0°c ∼ 18 hours. The oxygen-enhancement ratio (o.e.r.) measured at D50 for seedling growth reduction (dry weight per plant) ranged from 1·3 for onion to 16·7 for rice. The wide range in oxygen-sensitivity among species is not related to nuclear volume or interphase chromosome volume, the relative radiosensitivity of the species or any taxonomic criteria. The radiation damage appeared to be enhanced more by oxygen in starchy than in oily seeds. Seed radiosensitivity was related to nuclear and interphase chromosome volumes when seeds were soaked in nitrogen-bubbled water; however, the relationship did not exist for seeds soaked in oxygen-bubbled water.