Repair of Gamma-ray and Neutron-induced Lesions in Germinating Barley Seeds

Summary Barley seeds were irradiated with gamma-rays or fast neutrons in the resting state and after various periods of germination. When irradiated in the resting state, about 50 krads of gamma-rays or about 1 krad of fast neutrons produced a 50 per cent inhibition of seedling growth. The radiosensitivity increased after pre-soaking and reached a maximum level after 12-15 hours of germination. At this stage the sensitivity to gamma-rays had increased by a factor of 50 and to fast neutrons by a factor of 5. The presence of caffeine (assumed to be a DNA-repair inhibitor) during the first period of germination of seeds irradiated in the resting state led to an enhancement of the gamma-induced damage by a factor of 2, but had little effect on neutron-irradiated seeds. The caffeine effect was also negligible if the gamma-irradiated seeds were allowed to germinate for at least 5 hours in water before the treatment. The effect of caffeine was also considerably lower in seeds pre-soaked for 12-15 hours. The results are explained on the basis of (a) a differential distribution of lesions after gamma-ray and neutron irradiation and (b) a differential organization and mobility of the chromsome material in resting and germinating seeds.