Abstract
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.
Highlights
In recent decades, heavy metal contamination of soils, air, and water has increased and posing threats to agricultural ecosystems and environments globally due to rapid urbanization and industrialization
Mustard plants exposed to increasing doses of Pb showed a reduction in plant height, Fresh weight (FW), and dry weight (DW) at 30 days after sowing (DAS), 45 DAS, and at harvest
The greatest growth and biomass reductions (37% in height, 49% in FW, 24% in DW, 22% in primary branch number, and 36% in secondary branch number) compared to the control were observed at 45 DAS for plants treated with 1 mM Pb (Tab. 1 and Fig. 1)
Summary
Heavy metal contamination of soils, air, and water has increased and posing threats to agricultural ecosystems and environments globally due to rapid urbanization and industrialization. These metals can be taken up by plants from contaminated soil and by atmospheric deposition reducing plant growth and productivity. When lead becomes mobilized it can impact on seed germination and cause malformation of cellular structure, chlorosis, and stunted plant growth It blocks K+, Mg2+, Ca2+, Mn2+, Zn2+, Fe3+ to entry into the root system impacting on cellular functions and subsequently resulting in phytotoxicity to plants [3,4]
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