Modification of the radiosensitivity of barley seed by post-treatment with caffeine

Barley seeds of a hull-less variety (IB 65) were γ-irradiated (40 and 45 krad, 100 rad/sec) at 250C, and the seeds were post-hydrated for 12 hours at approximately 30C in oxygenated and oxygen-free water or caffeine solutions (3.8 x 10-4 to 3.8 x 10-2M). Measurements of 8-day seedling growth showed that the different caffeine concentrations applied during oxygenated or oxygen-free hydrations produced no observable effects on the growth of unirradiated seeds. All caffeine concentrations afforded protection for the irradiated seeds under oxygenated conditions, and potentiated the damage under oxygen-free conditions. A maximum radio-protection occurred at a caffeine concentration of 3.8 x 10-3M, whereas radiosensitization under oxygen-free conditions was concentration-dependent. Possible mechanisms are discussed. (U.K.)