Total reducing capacity of Arabidopsis thaliana upon salt stress

Soil salinity is a common abiotic stress factor. Salt stress in plants causes secondary oxidative stress, which is the result of increased generation of reactive oxygen species (ROS). The defense against oxidative stress is provided by the antioxidant system, which consists of enzymes and low molecular weight antioxidants. The amount of antioxidant compounds determines the total reducing capacity (TRC) of plant cell. The involvement of such compounds in the regulation of redox balance of the cell under conditions of acute salt stress is still studied poorly. Accordingly, in this study the influence of different concentrations of sodium chloride (50, 100 and 200 mM) on the TRC in Arabidopsis was investigated. 4,5-5 weeks old Arabidopsis plants growing in soil were used for the investigation. Leave rosettes were separated from the roots and the cutting place placed in liquid Murashige-Skoog medium (0,5x MS), supplemented with 50, 100 or 200 mM sodium chloride. After 4 hours of treatment with 50 mM sodium chloride a 10-fold increase in the content of Na+ in leaves was observed. Increasing the concentration of sodium in the incubation medium to 100 mM and 200 mM caused an even greater accumulation of these ions in the plant, namely 20 and 28 times higher, respectively, compared to the control. In addition, increasing the incubation time to 8 hours resulted in no further increase in the concentration of Na+ in plants. It was found that 4 hours of treatment with 50 mM NaCl resulted in increase of TRC by 22%. However, when the salt concentration was further increased to 100 and 200 mM the TRC decreased to 24-25% below the level of control plants. Reduction of TRC was observed also after 8 hours of treatment. Thus, Arabidopsis plants incubated for 4 hours in 50 mM solution activate antioxidants synthesis in leaves, which leads to a temporary increase of TRC that is higher than in control plants. However, increasing the intensity and/or duration of stress treatment causes a decrease of the TRC below the control level. The obtained data suggest that the gradual depletion of the antioxidants pool occurs in the early stages of acute salt stress.