Effect of Exogenous Treatment with 24-epibrassinolide on Antioxidant System Regulation in Wheat Roots under Copper Stress

Heavy metal exposure is commonly acknowledged as a primary constraint on plant growth. The beneficial impacts of 24-epibrassinolide (EBL), an important brassinosteroid (BR), in mitigating abiotic stresses have led to its recognition as a growth regulator in plants. The present research investigates the potential protective role of 24-epibrassinolide (10−9 M) treatments on some physio-biochemical parameters in durum wheat roots (Triticum turgidum durum, var. Karim) under copper (Cu) toxicity (100 μM). The supply of EBL to Cu-contaminated growth medium of wheat seeds counteracted the harmful effects of the heavy metal on root growth, attested by fresh weight and length increase, and reduced the Cu accumulation by 56% as compared to non-treated roots with EBL. This achievement seems to be mediated by the decrease of Cu-imposed hydrogen peroxide (H2O2) overproduction and the protection of sensitive biomolecules against oxidative injury. This protective effect is confirmed by the lowered content of malondialdehyde and carbonyl groups, as well as minimized lipoxygenase activity. Besides, EBL application improved the activity of superoxide dismutase (SOD), catalase (CAT), and ascorbate-glutathione cycle enzymes, as well as phenylalanine ammonia-lyase (PAL). Moreover, co-treatment with Cu + EBL induced an increase in ascorbate, glutathione, and proline contents. The improvement of the cellular redox state following EBL addition seems to counteract Cu-induced cell death. This study provides new insights into the mechanism by which BRs modulate root antioxidant systems under copper stress, highlighting a coordinated activation of enzymatic and non-enzymatic defence pathways that contribute to maintaining the cellular redox homeostasis and stress resilience.