Repair of radiation-induced single-strand breaks in DNA of barley embryo.

Repair of single-strand breaks induced by gamma-irradiation was studied in barley embryos. Nuclei were isolated from embryos at specified times after initiation of water absorption under different temperature conditions. From the shift of the peak of DNA in alkaline sucrose gradient, it was observed that clear repair of induced breaks occurred in the irradiated embryo during 2 h after soaking. However, this type of repair was not observed after 5 h up to 16 h, because natural degradation of DNA also occurred in the non-irradiated embryos. The estimated mol. wt. of DNA from the non-irradiated dry embryo was 0.93 X 10(-8) daltons; on the other hand, it was decreased to 0.15 X 10(-8) daltons by 30 kR of gamma-irradiation. This decreased mol. wt. recovered to 0.52 X 10(-8) daltons (64% recovery) after 2 h soaking at 25 degrees C. The repair observed in this experiment was not dependent on the regular synthesis of macromolecules, especially DNA.