Excess Zinc Supply Reduces Cadmium Uptake and Mitigates Cadmium Toxicity Effects on Chloroplast Structure, Oxidative Stress, and Photosystem II Photochemical Efficiency in Salvia sclarea Plants.

Salvia sclarea L. is a Cd ²⁺ tolerant medicinal herb with antifungal and antimicrobial properties cultivated for its pharmacological properties. However, accumulation of high Cd ²⁺ content in its tissues increases the adverse health effects of Cd ²⁺ in humans. Therefore, there is a serious demand to lower human Cd ²⁺ intake. The purpose of our study was to evaluate the mitigative role of excess Zn ²⁺ supply to Cd ²⁺ uptake/translocation and toxicity in clary sage. Salvia plants were treated with excess Cd ²⁺ (100 μM CdSO ₄ ) alone, and in combination with Zn ²⁺ (900 μM ZnSO ₄ ), in modified Hoagland nutrient solution. The results demonstrate that S. sclarea plants exposed to Cd ²⁺ toxicity accumulated a significant amount of Cd ²⁺ in their tissues, with higher concentrations in roots than in leaves. Cadmium exposure enhanced total Zn ²⁺ uptake but also decreased its translocation to leaves. The accumulated Cd ²⁺ led to a substantial decrease in photosystem II (PSII) photochemistry and disrupted the chloroplast ultrastructure, which coincided with an increased lipid peroxidation. Zinc application decreased Cd ²⁺ uptake and translocation to leaves, while it mitigated oxidative stress, restoring chloroplast ultrastructure. Excess Zn ²⁺ ameliorated the adverse effects of Cd ²⁺ on PSII photochemistry, increasing the fraction of energy used for photochemistry (Φ _PSII ) and restoring PSII redox state and maximum PSII efficiency ( F v / F m ), while decreasing excess excitation energy at PSII (EXC). We conclude that excess Zn ²⁺ application eliminated the adverse effects of Cd ²⁺ toxicity, reducing Cd ²⁺ uptake and translocation and restoring chloroplast ultrastructure and PSII photochemical efficiency. Thus, excess Zn ²⁺ application can be used as an important method for low Cd ²⁺ -accumulating crops, limiting Cd ²⁺ entry into the food chain.