Zinc and Manganese Impact on Cabbage (Brassica rapa) Cadmium Tolerance: Comparative Transcriptomic and Metabolomic Study

Background and Aims Zinc (Zn) and manganese (Mn), as essential micronutrients, exhibit competitive antagonism against cadmium (Cd) through cation transporter competition. The effects of Cd stress and Zn / Mn nutrition on plant growth, development, physiological characteristics, and gene expression in some crops have been widely studied, but the molecular mechanism by which Zn / Mn alleviates Cd toxicity in the roots of cabbage at the transcriptomic and metabolomic levels remains unclear. Methods The response of cabbage roots to Cd stress under Zn, Mn and ZnMn treatment were evaluated in an experiment with cabbage roots. The content of Cd was determined by ICP-MS. Roots transcriptome sequencing was performed on the Illumina platform, with differential expression genes (DEGs) analyzed using DESeq2. Root metabolites were analyzed via LC-MS, with metabolite data processed using MetaboAnalystR package. Results Zn treatment exhibited the strongest inhibition of Cd, primarily by up-regulating genes involved in cell wall synthesis, phenylpropanoid biosynthesis, and secondary metabolite production. Mn treatment had the weakest effect on Cd inhibition, mainly regulating hydrolase activity, tryptophan metabolism, and lipid metabolism to reduce Cd absorption in cabbage roots. ZnMn co-treatment showed a lower Cd inhibition rate than Zn, but it down-regulated numerous genes and disrupted amino acid metabolism, suggesting that while it reduces Cd content and may harms plant physiological functions. Conclusion This study highlights the potential of micronutrients resist Cd stress in crops, particularly in the leafy vegetables. Based on Cd reduction and plant physiological safety, we believe that Zn treatment is better than Mn treatment, and better than ZnMn co-treatment.