Exogenous salicylic acid-triggered changes in the glutathione transferases and peroxidases are key factors in the successful salt stress acclimation of Arabidopsis thaliana

Salicylic acid (SA) applied exogenously is a potential priming agent during abiotic stress. In our experiments, the priming effect of SA was tested by exposing Arabidopsis thaliana (L.) Heynh. plants to 2-week-long 10(-9)-10(-5) M SA pretreatments in a hydroponic medium, followed by 1 week of 100 mM NaCl stress. The levels of reactive oxygen species and H2O2, changes in antioxidant enzyme activity and the expression of selected glutathione transferase (GST) genes were investigated. Although 10(-9)-10(-7) M SA pretreatment insufficiently induced defence mechanisms during the subsequent salt stress, 2-week pretreatments with 10(-6) and 10(-5) M SA alleviated the salinity-induced H2O2 and malondialdehyde accumulation, and increased superoxide dismutase, guaiacol peroxidase, GST and glutathione peroxidase (GPOX) activity. Our results indicate that long-term 10(-6) and 10(-5) M SA treatment mitigated the salt stress injury in this model plant. Enhanced expression of AtGSTU19 and AtGSTU24 may be responsible for the induced GST and GPOX activity, which may play an important role in acclimation. Modified GST expression suggested altered signalling in SA-hardened plants during salt stress. The hydroponic system applied in our experiments proved to be a useful tool for studying the effects of sequential treatments in A. thaliana.