Metabolic disturbance in lettuce (Lactuca sativa) plants triggered by imidacloprid and fenvalerate

Intensive and indiscriminate use of insecticides in agroecosystems causes phytotoxic disturbances in non-target crops. However, the mechanisms by which plants reprogram cellular metabolites to resist and tolerate such agrochemicals remain unclear. Here, the interaction between lettuce plants with imidacloprid and fenvalerate was investigated by the complementary use of physiological and metabolomic analyses. Neither imidacloprid nor fenvalerate induced overt phytotoxicity in lettuce seedlings. The plant biomass, chlorophyll fluorescence, lipid peroxidation, and membrane integrity were not significantly affected by the selected insecticides. Flavonoid content decreased by 25% in lettuce leaves under fenvalerate exposure, whereas polyphenol and flavonoid contents were not significantly altered by imidacloprid. Although the content of most of the nutrient element in the leaves remained the same following pesticide treatment, iron content decreased by 28.1% under imidacloprid exposure but increased by 22.8% under fenvalerate exposure. Metabolomic analysis revealed that the selected insecticides induced extensive metabolic reprogramming in lettuce roots and shoots. Imidacloprid dramatically increased the metabolism of several amino acids (arginine, cysteine, homoserine, and 4-hydroxyisoleucine), whereas markedly decreased the metabolism of various carbohydrates (glucose, raffinose, maltotetraose, maltopentaose, and stachyose). Fenvalerate did not significantly alter amino acid metabolism but decreased carbohydrate metabolism. Additionally, the relative abundance of most organic acids and polyphenolic compounds decreased significantly after pesticide exposure. These results suggest that plants might program their primary and secondary metabolism to resist and tolerate insecticides. The findings of this study provide important information on how neonicotinoid and pyrethroid insecticides affect the health and physiological state of plants, which are ultimately associated with crop yield and quality.