The changes in peroxidase activity and organic acid content in wheat leaves exposed to salt-alkali stress

Background. Simultaneous exposure of plants to saline and alkaline stress induces feedback reactions directed at osmoregulation, pH regulation and protection against excess salt ions and oxygen radicals. It’s relatively hard to discriminate the toxic effect of salinity from the effect of high pH on plants. The purpose of the study was to determine the influence of salinity and alkalinity on peroxidase activity and organic acid content (reduced ascorbic acid, oxalic acid, malic acid, succinic acid, citric acid) in wheat leaves exposed to salt-alkali stress. Materials and methods. The object of the study is a soft spring wheat (Triticum aestivum L.). The two-factor experiment was conducted: plants were exposed to NaCl salinity (30 mM, 70 mM, 100 mM, 150 mM) and alkalinity (7, 8, 9, 10 pH). Plant samples were harvested 1h, 4h and 24h after exposure to stress. Peroxidase activity was determined according to Boyarkin; reduced ascorbic acid content was measured according to Chupakhina; oxalic, malic, succinic and citric acid concentrations were determined by HPLC. Results. The study determined the influence of salinity and alkalinity as well as its combined impact on parameters associated with the development of oxidative stress (peroxidase activity and reduced ascorbic acid), osmoregulation, pH-stat and ion balance (organic acids). Conclusions. In salt-alkali stress conditions NaCl concentration and alkalinity had the highest impact on the content of Krebs cycle acids in wheat leaves. The effect of these factors on peroxidase activity and oxalic acid content was slightly lower. The impact of both factors on reduced ascorbic acid content during the first hours of the experiment was low and didn’t reach significance by the end of the day. The impact of NaCl-salinity on peroxidase activity tended to be increased when compared to alkalinization. A pH value influenced organic acids content in wheat leaves to a greater extent than NaCl concentration.