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

Ilektra Sperdouli; Ioannis-Dimosthenis S Adamakis; Anelia Dobrikova; Emilia Apostolova; Anetta Hanć; Michael Moustakas

doi:10.3390/toxics10010036

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

Toxics. 2022 Jan 12;10(1):36. doi: 10.3390/toxics10010036.

Authors

Ilektra Sperdouli¹, Ioannis-Dimosthenis S Adamakis², Anelia Dobrikova³, Emilia Apostolova³, Anetta Hanć⁴, Michael Moustakas⁵

Affiliations

¹ Institute of Plant Breeding and Genetic Resources, Hellenic Agricultural Organization-Demeter, Thermi, 57001 Thessaloniki, Greece.
² Section of Botany, Department of Biology, National and Kapodistrian University of Athens, 15784 Athens, Greece.
³ Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria.
⁴ Department of Trace Analysis, Faculty of Chemistry, Adam Mickiewicz University, 61614 Poznań, Poland.
⁵ Department of Botany, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece.

Abstract

Salvia sclarea L. is a Cd²⁺ tolerant medicinal herb with antifungal and antimicrobial properties cultivated for its pharmacological properties. However, accumulation of high Cd²⁺ content in its tissues increases the adverse health effects of Cd²⁺ in humans. Therefore, there is a serious demand to lower human Cd²⁺ intake. The purpose of our study was to evaluate the mitigative role of excess Zn²⁺ supply to Cd²⁺ uptake/translocation and toxicity in clary sage. Salvia plants were treated with excess Cd²⁺ (100 μM CdSO₄) alone, and in combination with Zn²⁺ (900 μM ZnSO₄), in modified Hoagland nutrient solution. The results demonstrate that S. sclarea plants exposed to Cd²⁺ toxicity accumulated a significant amount of Cd²⁺ in their tissues, with higher concentrations in roots than in leaves. Cadmium exposure enhanced total Zn²⁺ uptake but also decreased its translocation to leaves. The accumulated Cd²⁺ 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 Cd²⁺ uptake and translocation to leaves, while it mitigated oxidative stress, restoring chloroplast ultrastructure. Excess Zn²⁺ ameliorated the adverse effects of Cd²⁺ on PSII photochemistry, increasing the fraction of energy used for photochemistry (Φ_PSII) and restoring PSII redox state and maximum PSII efficiency (Fv/Fm), while decreasing excess excitation energy at PSII (EXC). We conclude that excess Zn²⁺ application eliminated the adverse effects of Cd²⁺ toxicity, reducing Cd²⁺ uptake and translocation and restoring chloroplast ultrastructure and PSII photochemical efficiency. Thus, excess Zn²⁺ application can be used as an important method for low Cd²⁺-accumulating crops, limiting Cd²⁺ entry into the food chain.

Keywords: chlorophyll fluorescence; clary sage; hydrogen peroxide; hydroponic culture; non photochemical quenching; photosynthesis; phytotoxicity; quinone A (QA); reactive oxygen species; redox state.