ALLEVIATIVE EFFECTS OF EXOGENOUS SALICYLIC ACID ON SOME ANTIOXIDATIVE ENZYMES OF PISUM SATIVUM L. UNDER SODIUM FLUORIDE STRESS

The aim of the present study was to examine the effect of salicylic acid on the salinity tolerance of two varieties (RKS-510 and Classic) of pea (Pisum sativum L.). Sodium fluoride (NaF), in concentrations of 50, 100, 150, and 200 ppm, was applied, in a pot experiment during the growth season 2015-2016, to the plants as a soil drench on a biweekly basis to create a stressed condition by its gradual accumulation causing toxic effects on the biochemical processes of the plants. Salicylic acid, in concentrations of 100, 200, and 300 ppm, was also given exogenously to the fluoride-stressed plants as a foliar application to examine its effect on two anti-oxidative enzymes, ascorbate peroxidase and peroxidase. Control plants were treated with tap water. At 44 days after sowing (DAS), the activity of ascorbate peroxidase was lowest in the control plants for both cultivars (controls: 0.47 and 0.45 mu mol/min/g fresh weight for RKS-510 and Classic, respectively) and increased with increasing concentrations of NaF (50 ppm: 0.57 and 0.54; 100 ppm: 0.76 and 0.72; 150 ppm: 0.85 and 0.82; 200 ppm: 0.93 and 0.90 mu mol/min/g fresh weight for RKS-510 and Classic, respectively). Similarly, the activity of peroxidase was lowest in the control plants for both cultivars (controls: 0.27 and 0.25 units of enzyme activity g(-1) fresh weight min(-1) for RKS-510 and Classic, respectively) and increased with increasing concentrations of NaF (50 ppm: 0.35 and 0.32; 100 ppm: 0.38 and 0.35; 150 ppm: 0.44 and 0.43; 200 ppm: 0.49 and 0.47 units of enzyme activity g(-1) fresh weight min(-1) for RKS-510 and Classic, respectively). Compared to the NaF-treated group, the foliar application of the application of both salicylic acid (foliar application) and NaF (soil drench) lowered the fluoride-induced stress resulting in lower activity levels for ascorbate peroxidase and peroxidase. However, at higher concentrations, salicylic acid itself may cause a high level of stress in plants and was less effective. We concluded that the foliar application of salicylic acid has an ameliorative effect on the impaired salinity tolerance in the RKS-510 and Classic cultivars of Pisum sativum L. produced by sodium fluoride stress.