Physiological and biochemical responses of Italian basil to lead stress following salicylic acid and silicon-based treatments

Lead (Pb) contamination imposes severe constraints on the growth, physiology, and metabolic stability of medicinal plants. This study investigated the physiological and biochemical responses of Italian basil ( Ocimum basilicum L.) to Pb stress following treatment with salicylic acid (SA), potassium silicate, and a silica–salicylic acid formulation. Exposure to Pb markedly reduced plant growth traits, biomass accumulation, mineral balance, membrane stability, and photosynthetic pigment content, while intensifying oxidative stress. Application of SA- and silicon-based treatments significantly alleviated Pb-induced damage, with treated plants exhibiting improved plant height, root development, leaf area, fresh and dry biomass, and enhanced uptake of Si, Ca, and K. Improvements in relative water content and membrane stability were closely associated with increased activities of antioxidant enzymes, including guaiacol peroxidase, polyphenol oxidase, catalase, and ascorbate peroxidase, particularly under Pb stress conditions. In addition, treated plants showed elevated levels of phenolic and flavonoid compounds, along with increased essential oil percentage and yield, accompanied by shifts in major oil constituents. Multivariate analyses revealed coordinated improvements in growth performance and biochemical resilience in response to SA- and silicon-based treatments. Overall, the results demonstrate that salicylic acid and silicon-based treatments effectively mitigate lead-induced stress in Italian basil by enhancing physiological performance and reinforcing antioxidant-mediated biochemical responses.