Calcium attenuates cadmium toxicity in Cosmos bipinnatus through cell wall remodeling and metabolic regulation: A...

Cadmium (Cd) contamination poses a severe threat to plant growth and food safety. Calcium (Ca) is known to ameliorate heavy metal toxicity, but the integrated physiological and molecular mechanisms, particularly in herb ornamental plants used for phytoremediation, remain inadequately understood. This study investigated the protective role of Ca against Cd stress in Cosmos bipinnatus for Cd-polluted soil remediation. Physiological analyses demonstrated that Ca supplementation significantly attenuated Cd-induced growth inhibition, reducing oxidative damage, reducing MDA levels and enhancing antioxidant enzyme activities (SOD, POD, CAT). Ca application increased Cd accumulation in roots by 43.00% but reduced its translocation to shoots by 7.38%, indicating enhanced root sequestration. Crucially, Ca remodeled the root cell wall by increasing pectin and cellulose contents and promoting pectin demethylation via elevated pectin methylesterase (PME) activity, which consequently augmented Cd binding in the cell wall. Transcriptomic profiling revealed that Ca orchestrated a multifaceted defense response. Key up-regulated pathways included glutathione metabolism, and alpha-linolenic acid metabolism. Correspondingly, genes associated with auxin biosynthesis were upregulated, while those involved in lignin over-synthesis were downregulated, aligning with the observed physiological restoration and cell wall modulation. Our findings elucidate a synergistic mechanism whereby Ca enhances Cd tolerance in Cosmos bipinnatus by concurrently fortifying the apoplastic barrier via cell wall remodeling, activating intracellular antioxidant and chelation systems, and modulating phytohormone signaling. This study provides a theoretical foundation for utilizing Ca amendment to improve the efficiency of ornamental plants in the phytoremediation of Cd-contaminated environments.