Mutation Research 470 (2000) 1–9 A comparison of DNA repair using the comet assay in tobacco seedlings after exposure to alkylating agents or ionizing radiation Tomáš Gichner a , Ondˇ rej Ptᡠcek a , Diana A. Stavreva a , Elizabeth D. Wagner b , Michael J. Plewa b,∗ a Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Na Karlovce 1a, 160 00 Prague 6, Czech Republic b Department of Crop Sciences, College of Agricultural, Consumer and Environmental Sciences, University of Illinois at Urbana-Champaign, 1101 W. Peabody Dr., Urbana, IL 61801, USA Received 1 March 2000; received in revised form 19 May 2000; accepted 31 May 2000 Abstract 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 -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 72h 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 40Gy of -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 -induced DNA lesions are fully functional in non-replicating leaf cells and single and double strand breaks are rapidly repaired. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Nicotiana tabacum var. xanthi; Single cell gel electrophoresis; SCGE; Comet assay; -radiation; Ethyl methanesulfonate; EMS; N-ethyl-N-nitrosourea; ENU Abbreviations: EMS, ethyl methanesulfonate; ENU, N-ethyl-N-nitrosourea; SCGE, single cell gel electrophoresis; TX1, Nicotiana tabacum plant cell suspension culture 1. Introduction The single cell gel electrophoresis (SCGE) assay quantitatively measures DNA damage resolved as strand breaks in individual nuclei [1]. The kinetics of DNA repair have been studied using SCGE analysis ∗ Corresponding author. Tel.: +1-217-333-3614. E-mail address: m-plewa@uiuc.edu (M.J. Plewa). and measuring the reduction of DNA strand breakage as a function of recovery time. Almost all of these studies have involved mammalian cells [2–7]. The SCGE assay has been suggested as one method for monitoring human exposure to genotoxic agents [8]. Plant genetic assay systems are excellent in situ envi- ronmental monitors [9,10]. The processing and per- sistence of DNA damage as measured with the SCGE assay is important in determining whether plants 1383-5718/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S1383-5718(00)00081-4