Transcriptomic and ultrastructural insights into zinc-induced hormesis in wheat seedlings: Glutathione-mediated antioxidant defense in zinc toxicity regulation

Zinc (Zn), an essential nutrient element, exhibits hormesis in plants-beneficial at low doses but toxic at high concentrations. To understand the molecular mechanisms underlying this hormetic response with low-dose stimulation and high-dose inhibition in wheat, we conducted transcriptomic analysis under different Zn treatments. Low Zn concentration (50 μM) promoted plant growth by maintaining chlorophyll content, enhancing MAPK signaling, phytohormone signaling, glutathione metabolism, nitrogen metabolism, and cell wall polysaccharide biosynthesis. High Zn concentration (500 μM) induced ultrastructural damage and suppressed photosynthesis, chlorophyll metabolism, and secondary metabolisms, while upregulating glutathione metabolism. Molecular docking revealed that hydrogen bonds between Zn and antioxidant enzymes facilitated reactive oxygen species scavenging. Notably, exogenous glutathione (GSH) application enhanced wheat tolerance to Zn stress by strengthening the antioxidant defense system and improving photosynthetic capacity. Our findings elucidate the underlying mechanisms of Zn hormesis in wheat and demonstrate the application potential of glutathione in mitigating Zn toxicity, providing strategies for managing Zn-contaminated soils.