Hormesis effect of cadmium on pakchoi growth: Unraveling the ROS-mediated IAA-sugar metabolism from multi-omics perspective.

Previous research on cadmium (Cd) focused on toxicity, neglecting hormesis and its mechanisms. In this study, pakchoi seedlings exposed to varying soil Cd concentrations (CK, 5, 10, 20, 40 mg/kg) showed an inverted U-shaped growth trend (hormesis characteristics): As Cd concentration increases, biomass exhibited hormesis character (Cd5) and then disappear (Cd40). ROS levels rose in both Cd treatments, with Cd5 being intermediate between CK and Cd40. But Cd5 preserved cellular structure, unlike damaged Cd40, hinting ROS in Cd5 acted as signaling regulators. To clarify ROS controlled subsequent metabolic processes, a multi-omics study was conducted. The results revealed 143 DEGs and 793 DEMs across all Cd treatment. KEGG indicated among all Cd treatments, the functional differences encompass: "plant hormone signal transduction" and "starch and sucrose metabolism". Through further analysis, we found that under the influence of ROS, the expression of IAA synthesis and signaling-related genes was significantly up-regulated, especially under Cd5 treatment. This further facilitated the accumulation of reducing sugars, which provided more energy for plant growth. Our research results demonstrated the signaling pathway involving ROS-IAA-Sugar metabolism, thereby providing a novel theoretical basis for cultivating more heavy metal hyperaccumulator crops and achieving phytoremediation of contaminated soils.