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 µM).
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 detoxifcation 1 (AtDTX1) and A.
thaliana detoxifcation 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.