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 methanesulfo nate (EMS), N-ethyl-N-nitrosourea (ENU) and gamma-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 re duction of the SCGE tail moment values in nuclei isolated from leaves was o bserved 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 i nitial DNA lesions during cell division. After 24 h recovery, leaf nuclei f rom cells exposed to 20 or 40 Gy of gamma-radiation expressed complete DNA repair. These data indicate that DNA lesions induced by alkylating agents a re not readily repaired and persist beyond 4 weeks. Enzymes necessary to re pair gamma-induced DNA lesions are fully functional in non-replicating leaf cells and single and double strand breaks are rapidly repaired. (C) 2000 E lsevier Science B.V. All rights reserved.