Priming agents combat copper stress in wheat (Triticum aestivum L.) under hydroponic conditions: Insights in impacts on morpho–physio–biochemical traits and health risk assessment

In recent years, the use of priming agents, such as silicon, melatonin, salicylic acid, glycine betaine, and ascorbic acid has gained significant attention for their role in mitigating abiotic stresses across various plant species. While previous research has been conducted on the individual impact of silicon, melatonin, salicylic acid, glycine betaine, and ascorbic acid in metal stress resistance among various crop species, their combined effects in the context of heavy metal stressed conditions remain underexplored. Wheat (Triticum aestivum L.) seedlings was grown under the toxic concentration of copper (Cu) i.e., 100 µM which were applied with silicon, melatonin, salicylic acid, glycine betaine, and ascorbic acid under hydroponic conditions for 21 days. The research outcomes indicated that the toxic concentration of Cu in the nutrient solution notably reduced plant growth and biomass, photosynthetic pigments, and gas exchange attributes. However, Cu stress also induced oxidative stress in the plants by increasing malondialdehyde (MDA), hydrogen peroxide (H₂O₂) which also induced increased compounds of various enzymatic and non-enzymatic antioxidants, health risk index (HRI) and also the gene expression and sugar content. Furthermore, a significant increase in proline metabolism, the AsA-GSH cycle, and the pigmentation of cellular components was observed. Although, the application of different priming agents, such as silicon, melatonin, salicylic acid, glycine betaine, and ascorbic acid showed a significant increase in plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds, and their gene expression and also decreased oxidative stress and HRI. In addition, the application of different priming agents enhanced cellular fractionation and decreased the proline metabolism and AsA-GSH cycle in T. aestivum seedlings. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.