Nano-Selenium Alleviates Cd Stress in Cherry Tomato via Modulating Subcellular Distribution and Secondary Metabolism

Cadmium (Cd), a toxic heavy metal, harms plant growth and human health. This study shows that under hydroponic conditions foliar nano-selenium (SeNPs) spraying better alleviates Cd stress in cherry tomatoes than sodium selenate. It boosts seedling biomass, chlorophyll levels, and photosynthetic parameters, reduces malondialdehyde and proline levels in leaves, enhances superoxide dismutase, peroxidase, and catalase activities. Consistently, gene expression analysis revealed that SeNPs markedly upregulated antioxidant-related genes (CAT1, POD) and the auxin-regulating gene (IAA) in leaves. Importantly, SeNPs reduced the Cd translocation factor by 31.47% (vs. 19.24% for sodium selenate) and increased cell wall-bound Cd proportions (54% in leaves, 55% in roots), thereby restricting Cd migration to organelles. Metabolomic profiling further revealed that SeNPs induced stronger metabolic reprogramming than sodium selenate, with 116 unique differential metabolites identified (vs. 48 for sodium selenate). Key upregulated metabolites included amino acid derivatives, carbohydrates, and flavonoids, while downregulated ones were mainly heterocyclic compounds. Notably, SeNPs uniquely and significantly enriched the glycine, serine, and threonine metabolism pathway, which was absent in the sodium selenate treatment. These changes were primarily routed through plant secondary metabolism, ABC transporters, and amino acid (tryptophan, glycine, serine, phenylalanine) pathways. This study offers new mechanistic insights into mitigating heavy metal stress in cherry tomatoes via nanomaterial‑based metabolic modulation.