Treatment with 24-epibrassinolide mitigates NaCl-induced toxicity by enhancing carbohydrate metabolism, osmolyte accumulation, and antioxidant activity in Pisum sativum

A pot culture study was performed to evaluate the differences between salt-stressed pea (Pisum sativum L.) plants of tolerant (Climax and Samarina Zard) and sensitive (Ambassidar and PF-400) genotypes, and to determine whether treatment with 24-epibrassinolide (EBL) could enhance the accumulation of osmolytes and antioxidant activity and thereby induce tolerance in salt-stressed plants. Three-week-old seedlings were subjected to +NaCl (5 dS m(-1)) and -NaCl conditions (0 dS m(-1)). After 4 days of salt stress, the plants were sprayed with Milli-Q water or EBL (0.125 mg L-1). The plants were sampled at 32 days after sowing and at the final maturity stage. Half-strength Hoagland solution was used as the nutrient medium. Both the tolerant and sensitive plants subjected to saline condition showed decreases in germination percentage, embryo axis length, plant fresh/dry biomass, leaf area, chlorophyll content, relative water content (RWC), photosynthesis, rubisco content, rubisco activity, stomatal conductance, number of stomata, stomatal size, number of epidermal cells, and yield attributes and increases in lipid peroxidation, total phenolics content, proline content, glycine betaine content, total amino acids content, total soluble sugars content, sucrose content, sucrose phosphate synthase activity, sucrose synthase activity, and activities of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, and guaiacol peroxidase). Salt stress had a less deleterious effect on Climax and Samarina Zard than on Ambassidar and PF-400. The foliar application of EBL mitigated the deleterious effects of NaCl by improving growth, productivity, and gas exchange attributes and by further enhancing the concentrations of the above osmolytes and antioxidants, particularly in the tolerant genotypes. The enhanced concentrations of osmolytes and antioxidants may have induced salt tolerance in the plants subjected to saline conditions, resulting in improved growth, gas exchange attributes, and yield.