Investigation of the effects of exogenous applied citrulline on the response of wheat seedlings to copper stress

This study investigated the role of exogenously applied citrulline in alleviating the effects of copper stress in wheat. Seedlings were initially treated with 1 mM citrulline for 2 days and then exposed to 400 µM CuSO₄ for 3 days. Citrulline application was shown to reduce lipid peroxidation, endogenous hydrogen peroxide (H₂O₂), proline accumulation, and percent water loss, while increasing levels of potent non-enzymatic antioxidants, particularly glutathione (GSH) and phenolic compounds. This led to a more balanced activation of antioxidant enzymes such as superoxide dismutase (SOD), glutathione reductase (GR), and guaiacol peroxidase (GPX), resulting in a more efficient defense mechanism. The increased activity of catalase (CAT) further demonstrates the active engagement of enzymatic antioxidant defenses. Citrulline application alleviated copper stress, as evidenced by the downregulation of Copper Transporter 3-like (COPT3), Copper Transporter 6-like (COPT6), and Proline-5-Carboxylate Synthase (P5CS) genes. Furthermore, expression analysis of GS and GST genes demonstrated that citrulline enhances wheat's tolerance to copper stress by strengthening its glutathione-based antioxidant defense system. Consequently, exogenous citrulline serves as an effective stress alleviator by activating antioxidant responses and modulating the expression of key stress-responsive genes.