| Abstract | dc.description.abstract | Root growth, G2 length, and the frequency of aberrant mitoses and apoptotic nuclei were recorded after a
single X-ray irradiation, ranging from 2.5 to 40 Gy, in Allium cepa L. root meristematic cells. After 72 h of
recovery, root growth was reduced in a dose-dependent manner from 10 to 40 Gy, but not at 2.5 or 5 Gy
doses. Flow cytometry plus TUNEL (TdT-mediated dUTP nick end labeling) showed that activation of
apoptosis occurred only after 20 and 40 Gy of X-rays. Nevertheless, irrespective of the radiation dose,
conventional flow cytometry showed that cells accumulated in G2 (4C DNA content). Simultaneously, the
mitotic index fell, though a mitotic wave appeared later. Cell accumulation in G2 was transient and partially
reversed by caffeine, thus it was checkpoint-dependent. Strikingly, the additional G2 time provided by this
checkpoint was never long enough to complete DNA repair. Then, in all cases, some G2 cells with stillunrepaired
DNA underwent checkpoint adaptation, i.e., they entered into the late mitotic wave with chromatid
breaks. These cells and those produced by the breakage of chromosomal bridges in anaphase will reach the G1
of the next cell cycle unrepaired, ensuring the appearance of genome instability. | en |
