Foliar application of salicylic acid improves growth and yield attributes by upregulating the antioxidant defense system in Brassica campestris plants grown in lead-amended soils

Lead (Pb) toxicity causes a severe impact on plant growth and productivity. A protective role of salicylic acid (SA) is well known under different abiotic stress conditions. However, very little is known about the SA-induced Pb resistance mechanism. In this study, we investigated the effect of SA on mustard plants (Brassica campestris L.) under Pb-stress conditions. Plants were exposed to three levels of Pb amendment to the soil (0.25, 0.50, 1.00 mM), with or without SA (0.25 mM). Plant growth, yield attributes, and yield at harvest were reduced depending on the severity of the Pb stress. Exogenous application of SA improved plant growth and yield. Biochemical data revealed that Pb toxicity resulted in higher oxidative damage by reducing nonenzymatic antioxidants such as ascorbate and glutathione at the higher dose of Pb treatment. Antioxidant enzymes (ascorbate peroxidase - APX, monodehydroascorbate reductase - MDHAR, dehydroascorbate reductase - DHAR, glutathione reductase - GR, guaiacol peroxidase - POD, glutathione S-transferase - GST, and catalase - CAT) responses varied with the Pb doses. Both the nonenzymatic and enzymatic components of the antioxidant defense system were upregulated after application of SA, resulting in lower oxidative damage under Pb-stress conditions. Taken together, the results suggest that exogenous application of the SA mitigates Pb-induced oxidative damage and consequently results in better growth and yield in mustard plants.