Cadmium Tolerance in Tea Plants (Camellia sinensis): Physiological, Biochemical, and Molecular Insights

Cadmium (Cd), a toxic and mobile heavy metal, poses significant risks to agricultural systems due to industrial pollution. Tea plants (Camellia sinensis L.) efficiently absorb and accumulate Cd from soil, leading to contamination in leaves. Chronic consumption of Cd-laden tea can cause severe health issues, including neurological, reproductive, and immunological disorders, as well as increased cancer risk. Despite growing concerns, the molecular mechanisms of Cd stress response in tea plants remain poorly understood. Current research highlights key physiological adaptations, including activation of antioxidant defenses and modulation of secondary metabolite pathways, which influence tea quality. Cd disrupts photosynthesis, induces oxidative stress, and alters the biosynthesis of flavor-related compounds. Several critical genes involved in Cd transport (e.g., CsNRAMP5, CsHMA3, CsZIP1), sequestration (CsPCS1), and stress regulation (CsMYB73, CsWRKY53, CsbHLH001) have been identified, offering insights into molecular responses. This review systematically examines Cd dynamics in the soil-tea plant system, its effects on growth, photosynthesis, and quality, and the physiological and biochemical mechanisms underlying Cd tolerance. By consolidating recent findings on Cd-responsive genes and regulatory pathways, this study provides a theoretical foundation for breeding Cd-resistant tea varieties and ensuring production safety. Furthermore, it identifies future research directions, emphasizing the need for deeper mechanistic insights and practical mitigation strategies. These advancements will contribute to safer tea consumption and sustainable cultivation practices in Cd-contaminated regions.