Multiple defense networks in cadmium-excluding plants: from adaptive mechanisms to agricultural applications

Cadmium (Cd) contamination of agricultural soils poses a serious threat to global food safety. Unlike hyperaccumulators, Cd-excluding plants employ a multi-layered defense strategy to restrict Cd entry into shoots and edible tissues. Understanding this integrated exclusion network is critical for developing crops that are both safe and productive on contaminated soils.

This review synthesizes recent advances in Cd exclusion from the rhizosphere to the shoot interface, highlighting the roles of rhizosphere immobilization (via root exudates and microbes), internal multi-layered defenses (apoplastic barriers, transporter-mediated efflux, antioxidant buffering and endophyte-aided) and terminal foliar excretion. Crucially, we focused on the metabolic trade-offs and environmental dependencies that govern these defenses. We also compared the logic of "interception and containment" of excluders with the strategy of "mobilization and storage" of hyperaccumulators. Furthermore, we critically evaluated the translational pathways, including breeding and phytoexclusion-based safe production strategies, and the key obstacles (e.g., genotype and environment interactions, trait trade-offs) to deploy exclusion traits in sustainable agriculture.

Cadmium exclusion operates as a resource-aware system where low-cost extracellular barriers may be prioritized, escalating to energy-dependent intracellular sequestration when necessary. Although molecular mechanisms are increasingly clear, their coordination under field conditions and associated growth-defense trade-offs remain central and ongoing challenges. Translation depends on combining precision breeding for optimized exclusion traits with agronomic practices. Applying Cd-excluding plants in heterogeneous environments requires a systematic approach linking mechanistic insight, field testing and scalable management to ensure crop safety for food production, as well as to explore non-food valorization pathways, on Cd-contaminated soils.