Harnessing brassinolide signaling to fortify maize against nickel toxicity: An integrative perspective on stress alleviation and adaptive responses

• Nickel (Ni) toxicity disrupts amino acid metabolism in Zea mays seedlings. • EBR enhances antioxidant enzyme activities under Ni stress. • EBR elevates the contents of Pro, Glu, Cys, His, and Met amino acids. • mRNA levels of CYP and MRP genes increases with EBR, supporting Ni detoxification. This study investigates how 24-epibrassinolide (EBR, 10⁻² µM) alleviates nickel (Ni) toxicity in maize seedlings by examining its effects on antioxidant enzyme activity, amino acid composition, and the mRNA expression of cytochrome P450 ( CYP ) and multiple drug resistance protein ( MRP ) gene families. In the present work, Ni stress caused a significant increment in antioxidant enzyme activity and levels of oxidative markers, as well as total protein contents in 10-day-old Zea mays L. cv. 704 seedlings exposed to nickel chloride (NiCl₂.6H₂O) at 0, 5, 10, 25, 50, 100, and 250 (μM). These changes were accompanied by a decrease in key amino acids such as glutamine (Gln), tyrosine (Tyr), valine (Val), isoleucine (Ile), and leucine (Leu), indicating oxidative damage and metabolic disruption. The expression of CYP, MRP4 , and GT1 genes also increased under Ni stress, suggesting their role in Ni detoxification and transport. EBR treatment enhanced antioxidant enzyme activity and neutralized reactive oxygen species (ROS), and also increased Osmoprotectants along with radical scavenging capacity, while lowering levels of oxidative markers and Ni in plant tissues. Additionally, amino acids such as proline (Pro), histidine (His), cysteine (Cys), methionine (Met), glutamate (Glu), and aspartate (Asp) were elevated along with CYP and MRP gene families’ expression, contributing to osmotic regulation and stress tolerance. Our findings reveal that amino acid modifications and transcriptional regulation of CYP and MPR gene families are involved in EBR-mediated alleviation of Ni toxicity in maize, highlighting EBR as a promising strategy for mitigating Ni stress.