Silicon–salicylic acid nanocomposites modulate lead uptake and biochemical responses in basil (Ocimum basilicum L.) under severe Pb stress

Background Lead (Pb) contamination represents a serious constraint to plant growth, metabolic stability, and crop safety, particularly in medicinal and aromatic plants such as basil ( Ocimum basilicum L.). Silicon (Si) and salicylic acid (SA) are known to improve plant tolerance to abiotic stress; however, their combined application in nanocomposite (NCs) form may provide a more efficient strategy for reducing Pb toxicity and regulating plant biochemical responses. This study evaluated the potential of silicon–salicylic acid nanocomposites, (Si–SA NCs), to mitigate Pb–induced biochemical disturbances in basil under severe Pb stress and to assess their Pb removal capacity in aqueous systems. Results The synthesized Si–SA NCs were characterized using UV–Vis spectroscopy, dynamic light scattering (DLS), zeta potential analysis, FTIR, Raman spectroscopy, XRD, SEM, and TEM, confirming their successful formation and structural properties. The NCs also showed a biphasic SA release profile, indicating controlled–release behavior. Under severe Pb stress, 1000 mg kg −1 soil, basil plants exhibited marked increases in anthocyanin, proline, and soluble sugars, along with a reduction in total protein content. Among the tested treatments, Si–SA NCs most effectively moderated Pb–induced metabolic changes. They limited the increase in soluble sugars to 12%, compared with 61% in untreated Pb–stressed plants, and reduced protein loss to 9%, compared with 34% in the stressed control. Anthocyanin accumulation appeared to be mainly driven by Pb stress and was not significantly modified by the applied treatments. Si–SA NCs also decreased DTPA–extractable Pb in post-harvest soil by 37.3% compared with the Pb control and reduced Pb translocation from roots to leaves, resulting in a low translocation factor (TF ≈ 0.17). In aqueous conditions, the NCs achieved up to 60% Pb removal, outperforming Si or SA applied individually. Conclusion The findings suggest that Si–SA NCs can alleviate Pb–induced biochemical disturbances in basil, decrease chemically extractable Pb in soil, reduce Pb movement to the aerial parts, and contribute to Pb removal under aqueous conditions. Although these results indicate the potential of Si–SA NCs as a multifunctional nano–enabled system for Pb stress mitigation, further studies under field conditions and across different plant species and contamination levels are required to confirm their broader applicability.