MODIFICATION OF RADIOSENSITIVITY OF BARLEY SEED BY POST-TREATMENT WITH CAFFEINE .3. INFLUENCE OF DOSE OF IRRADIATION AND CONCENTRATION OF CAFFEINE

Data on 8 day seedling growth show that the different concentrations of caffeine applied during oxygenated or O2-free hydrations do not produce observable effects on the growth of unirradiated seeds. These data bring out the dramatic effects of caffeine on the irradiated seeds. Soaking the irradiated seeds in oxygenated and O2-free water causes the maximum and minimum levels of damage, respectively. All the concentrations of caffeine, in general, afford protection under the oxygenated conditions and potentiate the damage under the O2-free conditions (P = 0.01). Critical examination of the data, however, reveals that maximum radioprotection occurs at a caffeine concentration of 3.8 .times. 10-3 M, and a 10-fold increase or decrease in the concentration causes significant reduction in the level of protection (P = 0.05 to P = 0.01). Radiosensitization by caffeine under O2-free conditions is concentration-dependent, i.e., the higher the concentration, the larger is the magnitude of radiosensitization.