Chemical modification of postirradiation damage under varying oxygen concentrations in barley seeds

The influence of ascorbic acid, potassium permanganate and caffeine on the postirradiation seedling injury of dry barley seeds was studied, irradiated (350 Gy 60Co gamma-rays) in vacuo and post-hydrated with varying oxygen concentrations in the soaking medium. The oxygen concentration in the post-hydration medium (OCHG) was adjusted at 0%, 10%, 30%, 50%, 80% and 100%. A linear response between the seedling injury and O2 concentration in the range of 0-80% was observed. These chemicals potentiated, protected or exerted no effect, depending upon the OCHG. Thus, ascorbic acid did not exert any effect on seeds post-hydrated at OCHG of less than or equal to 30%, but afforded radio-protection at OCHG of greater than or equal to 50%. Caffeine, on the other hand, potentiated the postirradiation injury at OCHG of less than or equal to 30%, exerted no influence at OCHG of approximately 50% and afforded radioprotection at OCHG of greater than or equal to 80%. Potassium permanganate enhanced the injury at OCHG of less than or equal to 10%, exerted no effect at OCHG of approximately 30% and afforded radioprotection at OCHG of greater than or equal to 50%. The possible radiation-chemical events in the dry irradiated seeds following their post-hydration containing different OCHG and the three test chemicals which are known free radical scavengers are discussed.