Kinetics of single strand break repair is altered in the atlig1-RNAi lines. (A) Induction of SSBs by methyl methanesulfonate (MMS). Ten day old seedlings of Arabidopsis Col0 were treated with for 1 hour. Nuclei isolated from treated and untreated seedlings were analysed by the alkali/neutral version of comet assay and evaluated for comet formation. The mean percentage of DNA in the comet tail for 300 comets for each concentration of MMS are shown. Induction of SSBs is linear in the 0–2 mM MMS concentrations range (R2 = 0.9638 Col0 and R2 =0.9365 atlig1-RNAi respectively). (B) Time course of SSB repair in Col0 and atlig1-RNAi lines over 6 hour repair period. Background DNA damage in untreated (control) seedlings and damage after 1 hour treatment with 2mM MMS (t = 0) is similar in both lines. Contrary to wild type plants, the number of SSBs in atlig1-RNAiA increases for 60 minutes after the end of treatment suggesting delayed ligation during repair. (C) Kinetics of SSB repair. The percentage of SSBs remaining were calculated for 0, 20, 60, 180 and 360 minute repair time points after the treatment with 2 mM MMS. Maximum damage is normalised as 100% at t = 0 for all lines.