In situ detection of DNA fragmentation in histological sections of immature embryos treated with CPT. TUNEL assay on histological sections of untreated embryos (a, c, and e) and embryos treated with 50 μM CPT for 3 days (b, d and f). The TdT enzyme was omitted in the negative control (g), and the positive control included a DNaseI incubation (h). Arrows indicate stained nuclei. SC, scutellum. EA, embryo axes. C, coleoptile. LP, leaf primordium. R, radicle. Scale bars: = 100 μm.