A comparison of DNA repair using the comet assay in tobacco seedlings after exposure to alkylating agents or ionizing radiation

We employed single cell gel electrophoresis to analyze the kinetics of DNA repair in nuclei isolated from tobacco plants exposed to ethyl methanesulfonate (EMS), N-ethyl-N-nitrosourea (ENU) and γ-radiation. DNA repair was measured as the reduction of the tail moment values as a function of time after the mutagen treatment ended. DNA damage in leaf nuclei of EMS- or ENU-treated tobacco plants persisted over a 72 h recovery period. However, a reduction of the SCGE tail moment values in nuclei isolated from leaves was observed over a 4-week period of recovery. Newly emerged leaves expressed a lower level of DNA damage due to more efficient repair and/or dilution of initial DNA lesions during cell division. After 24 h recovery, leaf nuclei from cells exposed to 20 or 40 Gy of γ-radiation expressed complete DNA repair. These data indicate that DNA lesions induced by alkylating agents are not readily repaired and persist beyond 4 weeks. Enzymes necessary to repair γ-induced DNA lesions are fully functional in non-replicating leaf cells and single and double strand breaks are rapidly repaired. (C) 2000 Elsevier Science B.V.