Bivariate BrdUrd/PI labeling of DNA with flow cytometric analysis. Contour plots showing cells with and without BrdUrd labeling after one hour and six hours of BrdUrd incubation. Cells were pulsed with BrdUrd for one hour or six hours after treatment with or without PSP (25 μg/ml) for 72 hours. Cells at G0/G1 and G2/M are BrdUrd negative labeled. Most of the S-phase cells actively undergoing DNA synthesis were labeled with BrdUrd. The one hour BrdUrd-labeled cells progressed through G2/M phase; divided after six hours of BrdUrd labeling and reappeared in the G0/G1 phase (6 hours BrdUrd labeled cells). These cells are called labeled divided cells (Ld) and the remaining S-phase cells are called labeled undivided cells (Lud). Values are expressed as mean (SD) (n = 5). * P < 0.05; ***P < 0.001, vs. control.