Chitosan/ZnO nanocomposites for improving the growth and reducing the toxicity of Zn in Sorghum bicolor (L.) Moench plants

The study investigates the dual function of chitosan/zinc oxide nanocomposites (CS/ZnO NCPs) in enhancing plant growth and mitigating zinc oxide nanoparticles (ZnO NPs) toxicity. While ZnO NPs hold promise for agriculture, concerns exist regarding their potential harm to plants and the environment. Incorporating ZnO NPs into a CS matrix to form CS/ZnO NCPs offers a solution. The metal-chelating properties of CS can regulate the release of Zn²⁺ ions from the NPs, reducing their availability to plants and mitigating potential toxicity. In the present work, the effect of ZnO NPs and CS/ZnO NCPs at two different concentrations, i.e., 100 and 200 ppm, has been tested on Sorghum bicolor plants. The ZnO NPs and CS/ZnO NCPs were chemically synthesized and characterized with various microscopic and spectroscopic techniques. Plants grown in ZnO NPs-treated soil for 30 days exhibited reduced growth, decreased chlorophyll, starch, and cellulose levels as well as nutrient (K, Mg and P) uptake. In addition, these nanoparticles increased malondialdehyde (MDA) content and the activities of antioxidant enzymes in the shoots, indicating their phytotoxicity to S. bicolor plants. Conversely, CS/ZnO NCPs application stimulated plant growth, nutrient uptake, chlorophyll and starch contents, while reducing MDA content and superoxide dismutase activity. The CS/ZnO NCPs-treated plants also accumulated 2.5–3.5 times less Zn²⁺ than ZnO NP-treated plants. Results of the study established that utilizing ZnO NPs in the form of CS/ZnO NCPs can maximize the beneficial characteristics of both nanomaterials while simultaneously limiting the toxic effects of ZnO on S. bicolor plants.