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.