Root initials and their early descendants are preferentially killed in response to DNA damage. Root initials and their early descendants are preferentially killed in response to DNA damage. (A) Diagram of the root meristem with the QC marked in green and root initials marked in red. (B–I) Representative confocal images of root tips stained with PI (B–D and G–I), which marks the outline of living cells but enters dead cells, or Sytox Orange (E and F), which stains dead cells. WOX5:GFP roots untreated (B) or after 24 h in 20 μg/mL zeocin (C); CYCB1;1-GFP root after 24 h in 20 μg/mL zeocin (D); roots expressing the plasma membrane marker LTI6b, untreated (E) or after 24 h in 20 μg/mL zeocin (F); WT 24 h after 40 Gy of x-rays (G); and untreated lig4–4 (H) and untreated ku80 (I) mutants. Arrows and asterisks indicate the QC and dead cells, respectively. (Scale bars: 50 μm.)‏ Nick Fulcher, and Robert Sablowski PNAS 2009;106:49:20984-20988 ©2009 by National Academy of Sciences