Temperature-effect on the repair of gamma-induced lesions in barley seeds

Abstract

Barley seeds were exposed to gamma-irradiation plus caffeine post-treatment under various temperatures (0–30°C) and examined for growth reduction, chromosomal aberrations and chlorophyll mutation. DNA synthesis and release of reducing sugars during the germination of non-irradiated seeds at different temperatures were also determined. The dose-response curve for 7-day-old seedling height was approximated by the standard function, F( D) = 0.9077 [1−(1−e − a 1 D ) 5]+0.0923, where F( D) = per cent of control in seedling height, D = radiation exposure, e = base of natural algorithm and a 1 = sensitivity coefficient. The extent of repair, expressed as the ratio of the difference between D 50 for seedling height with and without caffeine treatment of D 50 with irradiation alone, depended on the incubation temperature during the period from 3 hr to 27 hr after soaking. The initiation of sugar-release and 3H-thymidine incorporation was delayed in seeds exposed to 0°C and 10°C; a 30°C-exposure disturbed cellular metabolism and DNA sythesis as evidenced by reductions in sugar-release and 3H-thymidine incorporation. Mutation frequency and spectra after the gamma-ray and caffeine treatment were significantly stimulated by exposure to higher temperatures. It is concluded that thermal potentiation results from the depression of physiological reversion, affecting post-replication repair of gamma-induced lesions, and also that the increase in mutations with temperature is caused by a partial alteration in the conditions inhibiting DNA repair.