Zinc sulfide nanoparticles regulate cadmium toxicity in maize ( <i>Zea mays</i> L.) by improving Cd/Zn homeostasis

In the current study, we synthesized nano zinc sulfide (nZnS) and studied the effects of root zone (RZ) and foliar application (FS) of nZnS (0 and 50 mg/L) on cadmium (Cd) stressed maize (0 and 1 mM CdCl₂) using completely randomized design (CRD). After 20 d of nZnS supplementation, growth and biochemical responses were recorded. The study highlights the critical issue of Cd stress in maize and investigates how nZnS influences plant tolerance mechanisms. We explored the novelty of application of RZ and FS of nZnS, focusing on its role in Cd/Zn homeostasis, growth and stress resilience. The RZ supplementation with nZnS recovered growth and enhanced maize protein and phenolic content under Cd stress. Exogenous application of nZnS improved chlorophyll under Cd stress. Whereas, exposure to Cd stress markedly reduced Zn in shoots (0.0015 mg/g DW; -99.1%) compared to the control (0.186 mg/g DW). The nZnS application enhanced Zn fraction in shoots (2.03 mg/g DW by RZ; and 1.46 mg/g DW by FS), especially in Cd-stressed plants (2.68 mg/g DW by RZ; and 2.36 mg/g DW) by FS. Exposure to Cd stress resulted in an increased shoot Cd fraction (0.376 mg/g DW), which was further increased by root zone nZnS supply (0.673 mg/g DW; +44.0% compared to Cd-stressed plants. Foliar application of nZnS also enhanced the Cd concentration in the shoots (0.579 mg/g DW; +35.0% compared to the Cd-stressed plants). Although the Cd fraction was synergistically increased due to nZnS supply which can be explained based on Cd/Zn homeostasis reinforced by sulfur (S) supply. In conclusion, the use of nZnS alleviated Cd stress in maize, suggesting that it is an effective strategy for improving Cd tolerance in crops like maize.