Enantioselective Effects of Napropamide on Nutrient-Mediated Secondary Metabolite Biosynthesis and Cadmium Accumulation in Plants

Global industrialization has made soil heavy metal pollution a critical environmental issue, threatening human health. In many agricultural fields, heavy metal contamination coexists with herbicides, worsening crop safety risks. This study investigated napropamide (NAP) enantiomers' differential effects on plant growth, nutrient, secondary metabolites, and cadmium (Cd). Compared to the control, R-NAP significantly promoted plant growth and increased Cd accumulation, while S-NAP inhibited growth. Moreover, NAP treatments altered the secondary metabolites, particularly flavonoids and quinones. These metabolites might be regulated by macro- and micronutrients, thereby influencing plant Cd content. Furthermore, flavonoid- and quinone-related genes (e.g., OMT1 and 4CL3) were significantly upregulated under R-NAP treatments. Core metabolites strongly associated with these genes and Cd content, confirming their role in Cd accumulation. This work elucidates how NAP enantiomers regulate nutrient-mediated secondary metabolism against Cd stress, offering insights for controlling Cd accumulation in slightly to moderately contaminated soils under herbicide use.