Metabolomics to Detect Response of Lettuce (<i>Lactuca sativa</i>) to Cu(OH)<sub>2</sub> Nanopesticides: Oxidative Stress Response and Detoxification Mechanisms

There has been an increasing influx of nanopesticides into agriculture in recent years. Understanding the interaction between nanopesticides and edible plants is crucial in evaluating the potential impact of nanotechnology on the environment and agriculture. Here we exposed lettuce plants to Cu­(OH)<sub>2</sub> nanopesticides (1050–2100 mg/L) through foliar spray for one month. Inductively coupled plasma-mass spectrometry (ICP-MS) results indicate that 97–99% (1353–2501 mg/kg) of copper was sequestered in the leaves and only a small percentage (1–3%) (17.5–56.9 mg/kg) was translocated to root tissues through phloem loading. Gas chromatography-time-of-flight mass spectrometry (GC-TOF-MS) based metabolomics combined with partial least squares-discriminant analysis (PLS-DA) multivariate analysis revealed that Cu­(OH)<sub>2</sub> nanopesticides altered metabolite levels of lettuce leaves. Tricarboxylic (TCA) cycle and a number of amino acid-related biological pathways were disturbed. Some antioxidant levels (cis-caffeic acid, chlorogenic acid, 3,4-dihydroxycinnamic acid, dehydroascorbic acid) were significantly decreased compared to the control, indicating that oxidative stress and a defense response occurred. Nicotianamine, a copper chelator, increased by 12–27 fold compared to the control, which may represent a detoxification mechanism. The up-regulation of polyamines (spermidine and putrescine) and potassium may mitigate oxidative stress and enhance tolerance. The data presented here provide a molecular-scale perspective on the response of plants to copper nanopesticides.