Exogenous Application of 24-Epibrassinolide Improves Manganese Tolerance in Arabidopsis thaliana L. via the Modulation of Antioxidant System

The goal of the present study was to investigate the role of 24-Epibrassinolide (EBL) hormone in supporting adaptation of plant to manganese (Mn) stress. For this purpose, changes in antioxidant system and stress-related gene expression were determined in rosette leaves of Arabidopsis thaliana following 24-h exposure to Mn (0.5 and 1.0 mM) and/or EBL (1 mu M). Decreased chlorophyll level in the rosette leaves of seedlings due to Mn stress increased consequent to exogeneous EBL application. Superoxide dismutase (SOD) and catalase (CAT) enzyme activities alongside transcript level of copper/zinc superoxide dismutase 1 (CSD1), copper/zinc superoxide dismutase 2 (CSD2), copper/zinc superoxide dismutase 3 (CSD3), Fe superoxide dismutase 2 (FSD2), Fe superoxide dismutase 3 (FSD3), and catalase 2 (CAT2) genes were found to increase depending on Mn concentration; however, co-exposure of EBL and Mn led to a further improvement in enzyme activities and gene expressions (except CSD1 and CSD2 genes). The mRNA level of Fe superoxide dismutase 1 (FSD1) gene was downregulated following Mn and/or EBL treatments. Exogenous treatment of EBL improved the total antioxidant and proline level, while it decreased the lipid peroxidation under Mn stress. EBL treatment upregulated transcript level of delta 1-pyrroline-5-carboxylate synthase 1 (P5CS1) and delta 1-pyrroline-5-carboxylate synthase 2 (P5CS2) genes in seedlings treated with Mn. Co-treatment of Mn and EBL enhanced expression level of A. thaliana detoxification 1 (AtDTX1) and A. thaliana detoxification 3 (AtDTX3) genes when compared to the seedlings treated with Mn. Biochemical and molecular results from the current study revealed that EBL regulates antioxidant system in a coordinated manner under A. thaliana Mn stress.