Post-replication DNA repair in barley embryos treated with N-methyl-N-nitrosourea

In sterile cultures of free barley embryos, N-methyl-N-nitrosourea (MNU) caused a decrease in the size of both template [¹⁴C]-labeled DNA and of daughter [³H]DNA strands as determined in alkaline sucrose gradients, and inhibited the rate of [³H]thymidine incorporation. In addition, duplexes containing [³H]-daughter DNA analyzed in BND cellulose contained more single-stranded regions in MNU-treated embryos than in the corresponding control. Incubation of MNU-treated embryos in nutrient medium for up to 18 h after the [³H]-labeling permitted the recovery of small-sized daughter DNA to full-sized strands and led to the enhancement of double-strandedness of DNA duplexes containing [³H]-labeled strands. If [³H]-labeling had been carried out 8–10 h after the MNU treatment, the size of daughter DNA, the proportion of double-strandedness and the rate of thymidine uptake into DNA partially increased in comparison with rates observed when labeling had been done just after or 3 h after the MNU treatment, but these variables did not reach the values of the corresponding controls.