الملخص

Abstract The present study was conducted to determine the effects of gamma rays on specific activity of dihydrofolate reductase and folate content of Black seed (Nigella sativa L.) callus. The effect was dependent on doses of gamma rays. The obtained results showed that specific activity of dihydrofolate reductase increased with the growth period at doses 5, 10, 30 and 50 rad, the total folate content increased substantially, but the high doses of rays (70, 90 rad) led to decrease of dihydrofolate reductase activity and folate content extracted from callus of different ages. On the other hand, the results revealed that the exposed callus at 5 rad exhibited high level resistance to 10-1 M of aminpterin and trimethoprime. The specific activity of dihydrofolate reductase and total folate content were partly reserved as a result of radiation compared with non-radiated callus.