24-Epibrassinolide mitigates arsenate stress in seedlings of Oryza sativa (IR-20) via the induction of phenylpropanoid pathway

The introduction of arsenic, a hazardous metalloid, into the soil system due to heavy industrialization has negatively affected agricultural productivity, resulting in limited crop yields. A recent breakthrough in stress-responsive hormones, specifically brassinosteroids, has extensively covered the role of antioxidant enzyme defense systems in heavy metal stress mitigation. Considering the antioxidant properties and metal complex formation abilities of polyphenols, our study focuses on examining their role in arsenate toxicity amelioration by 24-epibrassinolide. We demonstrate enhanced growth parameters of sodium arsenate-stressed seedlings upon application of 24-epibrassinolide, with increased root and shoot polyphenol levels analyzed by high-performance liquid chromatography. Specifically, the concentration of catechin, sinapic acid, 4-hydroxy benzoic acid, protocatechuic acid, 4-coumaric acid, and myricetin were elevated, indicating induction of phenylpropanoid signaling pathway. Further, we also report a decrease in the generation of superoxide anions and hydrogen peroxide validated the antioxidant effects of these metabolites through the nitrobluetetrazolium and diaminobenzidine staining method. In addition, evaluation of transcript level of genes encoding for specific enzymes of the phenylpropanoid pathway in shoot and root showed a significant upregulation in mRNA expression of phenylalanine ammonia-lyase-1, cinnamate-4-hydroxylase, and caffeic acid o-methyltransferase-1 upon exogenous application of 24-epibrassinolide in arsenate stressed Oryza sativa.