Barley seed radiosensitivity following post-hydration in oxygen-, nitrogen- and nitrous oxide-saturated water. I. Influence of caffeine and t-butyl alcohol.

Dry (approximately 3.5 and 4.0 per cent moisture content) barley seeds were exposed to 350 Gy of 60Co- gamma-rays in vacuo and post-hydrated at 4 degrees C for 8 h in O2-, N2-, or N2O-saturated water. The effect of caffeine and t-butyl alcohol (t-BuOH) dissolved in the post-hydration medium on the magnitude of damage developing under these three different gaseous circumstances was studied. The post-irradiation damage and its modification by caffeine and t-BuOH was assessed in terms of 8-day-old seedling injury, peroxidase activity and total peroxides in the 8-day-old seedlings. Post-irradiation O2-saturated hydration caused maximal 8-day-old seedling injury, and increased peroxidase activity with concomitant reduction in total peroxides. Both caffeine and t-BuOH afforded significant radioprotection against post-irradiation O2-dependent damage. Post-irradiation N2O-saturated hydration was even more significantly radioprotective than the N2-saturated post-hydration. Under these circumstances, t-BuOH exerted no effect whatsoever on the N2- and N2O-mediated post-irradiation damage. Caffeine, on the other hand, significantly potentiated these two components of damage. A brief consideration of the physicochemical events which possibly account for the observed effects is presented.