Lysine-metal complexes modulate nutrient and gene responses in Pb-stressed maize (Zea mays L.)

Lead (Pb) toxicity significantly undermines agricultural productivity and food safety by disrupting plant growth and vital physiological functions, highlighting the urgent need for innovative approaches to enhance nutrient uptake and utilization. In this context, the use of lysine-metal complexes emerges as a crucial strategy, not only mitigating Pb toxicity but also optimizing mineral nutrient acquisition in plants, thereby supporting essential physiological processes and improving overall plant resilience. This study investigated the efficacy of lysine-metal complexes (copper-lysine [Cu-Lys], magnesium-lysine [Mg-Lys], and calcium-lysine [Ca-Lys]) in alleviating Pb-induced stress in maize (Zea mays L.) through the enhancement of growth attributes, photosynthetic efficiency, antioxidant defense, and cellular mechanisms. A pot experiment was conducted at Zayed University, UAE, where Pb was applied at 0, 100, and 200 mg kg^-1 soil using Pb(NO₃)₂, and foliar treatments of Lys-metal complexes (10 mg L^-1) were applied weekly, starting 14 days after sowing. The results revealed that Pb stress significantly reduced plant growth, photosynthetic pigments, gas exchange, and biomass, accompanied by increased oxidative stress markers such as hydrogen peroxide and malondialdehyde. However, Lys-metal complexes, particularly copper-lysine complex (Cu-Lys), markedly improved growth, photosynthetic pigments, gas exchange parameters, and antioxidant activities, including the AsA-GSH cycle and enzymatic antioxidants (superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase). Proline accumulation and modulation of cellular fractionation were observed, leading to reduced Pb translocation and enhanced Pb immobilization in the cell wall. Among the treatments, Cu-Lys demonstrated superior effectiveness, followed by magnesium-lysine complex (Mg-Lys) and Ca-Lys. In conclusion, Lys-metal complexes mitigate Pb toxicity by improving physiological and biochemical responses, reducing Pb uptake, and enhancing antioxidant defense mechanisms. These findings highlight the potential of Cu-Lys, Mg-Lys, and Ca-Lys as sustainable strategies to enhance Z. mays resilience in Pb-contaminated environments.