Comparative proteomic analysis of CPT-induced DNA damage in maize immature embryos. 2-D gel electrophoresis of untreated (A) and camptothecin-treated (B) maize embryos showing the localisation of the spots identified by mass spectrometry. The pH gradient, 3 to 11, is indicated on the top axis and molecular masses on the left. Spots that were excised and identified by mass spectrometry are labeled with spot ID numbers [U1-16, spots up-accumulated by CPT treatment; D1-14, spots down-accumulated by CPT treatment] listed in Table 3. (C) Portions of 2-D gels showing spots (arrows) that were differentially abundant between untreated (CON) and treated (CPT) embryos.