Arabidopsis thaliana contains 54 soluble glutathione transferases (GSTs, EC 2.5.1.18), which are thought to play major roles in oxidative stress responses, but little is known about the function of individual isoenzymes. The role of AtGST phi 9 (GSTF9) in the salt- and salicylic acid response was investigated using 2-week-old Atgstf9 and wild type (Wt) plants. Atgstf9 mutants accumulated more ascorbic acid (AsA) and glutathione (GSH) and had decreased glutathione peroxidase (GPOX) activity under control conditions. Treatment of 2-week-old seedlings with 10⁻⁷ M salicylic acid (SA) for 48 h resulted in elevated H₂O₂level and enhanced GST activity in Atgstf9 plants, 10⁻⁵ M SA treatment enhanced the malondialdehyde and dehydroascorbate contents compared to Wt. 50 and 150 mM NaCl increased the GST activity, AsA and GSH accumulation in Atgstf9 seedlings more pronounced than in Wt plants. We found that the Atgstf9 mutants had altered redox homeostasis under control and stress conditions, in which elevated AsA and GSH levels and modified GST and GPOX activities may play significant role. The half-cell potential values calculated from the concentration of GSH and GSSG indicate that this GST isoenzyme has an important role in the salt stress response.
Keywords: Arabidopsis thaliana; ascorbic acid; glutathione; glutathione peroxidase activity; glutathione transferase phi 9.