Abstract: Salinity is an important limiting environmental factor for rapeseed production worldwide. In this study, we assessed the extent and pattern of DNA damages caused by salt stress in rapeseed plants. Amplified fragment length polymorphism (AFLP) analysis revealed dose-related increases in sequence alterations in plantlets exposed to 10–1 000 mmol/L sodium chloride. In addition, individual plantlets exposed to the same salt concentration showed different AFLP and selected region amplified polymorphism banding patterns. These observations suggested that DNA mutation in response to salt stress was random in the genome and the effect was dose-dependant. DNA methylation changes in response to salt stress were also evaluated by methylation sensitive amplified polymorphism (MSAP). Three types of MSAP bands were recovered. Type I bands were observed with both isoschizomers Hpa II and Msp I, while type II and type III bands were observed only with Hpa II and Msp I, respectively. Extensive changes in types of MSAP bands after NaCl treatments were observed, including appearance and disappearance of type I, II and III bands, as well as exchanges between either type I and type II or type I and type III bands. An increase of 0.2–17.6% cytosine methylated CCGG sites were detected in plantlets exposed to 10–200 mmol/L salt compared to the control, and these changes included both de novo methylation and demethylation events. Nine methylation related fragments were also recovered and sequenced, and one sharing a high sequence homology with the ethylene responsive element binding factor was identified. These results demonstrated clear DNA genetic and epigenetic alterations in plantlets as a response to salt stress, and these changes may suggest a mechanism for plants adaptation under salt stress.

Key words: Brassica napus, DNA-methylation, genetic variation, methylation sensitive amplified polymorphism, salt stress.