Zinc contamination in soils and its implications on plant phytoalexins

Abstract Zinc (Zn) toxicity in soils, uptake, translocation, and its effects on plant phytoalexins (low-weight molecular bioactive substances) are well-elucidated, as such studies scarcely exist. Excess Zn can predominantly accumulate in soils through anthropogenic interferences, mainly from metallurgy (mining and smelting). The distribution of Zn in the soil solution occurs as Zn-organic matter (organically complexed), labile (inorganic ion pairs), and free Zn 2+ , readily accessible to plants. As a microelement, excess Zn accumulation can result in plant toxicity in the high metabolic parts, including the leaf, root, and seed. Hence, Zn stress affects plants’ metabolic pathways, resulting in poor growth and productivity. As an abiotic elicitor, excess Zn contributes to the synthesis of low molecular weight compounds- plant phytoalexins (non-enzymatic components with antioxidant and antimicrobial properties), which prevent oxidation of essential biomolecules. Antioxidant responses to Zn stress depend mainly on Zn content, exposure time, plant species or ecotype, and organs. However, Zn stress reduces enzymatic activities in detoxifying reactive oxygen species and distorts the antimicrobial properties of phytoalexins. Phytoalexins, including kievitone [C 20 H 20 O 6 ] and glyceollin [C 20 H 18 O 5 ]) possess health-promoting effects on humans (disease resistance) due to their antimicrobial, antifungal, and antioxidant properties in pharmacology and as food sources. Hence, a detailed chemical analysis of phytoalexins from plants contaminated with Zn is vital due to ecotoxicological effects. This interdisciplinary study permits readers to acknowledge the level of development under this topic and existing gaps where current knowledge is well-established in soils and plant systems.