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

Abstract

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)2 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)2 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.

Comparative environmental fate and toxicity of copper nanomaterials

“…These early growth stage results indicate some noticeable effects from all Cu NPs, although no clear pattern was exhibited with regards to toxicity ranking based on physiological or biochemical indicators. Lettuce grown from seed to maturity in soil, and exposed through foliar spray to nCu(OH) 2 -b during the last 4 weeks before harvesting at 1050 mg/L to 2100 mg/L, exhibited no visible damage (Zhao et al, 2016b). In fact, leaf biomass, which is the harvestable product, increased significantly (p < 0.05).…”

“…For example, lettuces exposed to nCu(OH) 2 -b, following the recommended application amount, accumulated around 1350-2010 mg Cu/ kg dry weight (DW) after 30 days of foliar exposure. The accumulated Cu was mostly inside the tissues, since the lettuces were washed thoroughly (Zhao et al, 2016b). While most of the copper (97-99%) was sequestered in the leaves, a small fraction (1-3%, 17.5-56.9 mg/ kg) was translocated to root tissues through phloem loading (Zhao et al, 2016b).…”

“…The accumulated Cu was mostly inside the tissues, since the lettuces were washed thoroughly (Zhao et al, 2016b). While most of the copper (97-99%) was sequestered in the leaves, a small fraction (1-3%, 17.5-56.9 mg/ kg) was translocated to root tissues through phloem loading (Zhao et al, 2016b). A fraction was in the form of nano-and microparticulates, although not necessarily as Cu(OH) 2 .…”

“…mussels) that pack and excrete Cu (ion and NPs) in pseudofeces (Hanna et al, 2013;Montes et al, 2012), in fish (Abdel-Khalek et al, 2016), marine invertebrates , and in terrestrial plants (Hong et al, 2014;Zhao et al, 2016a;Zhao et al, 2016b;Zhao et al, 2016c). While it is likely that Cu is internalized as Cu 2 + or in organic complexes, in some cases Cu NPs are ingested or taken up from soil into the organisms, where they likely dissolve.…”

“…In fact, leaf biomass, which is the harvestable product, increased significantly (p < 0.05). However, metabolomics analysis revealed that nCu(OH) 2 -b altered metabolite levels in the lettuce leaves (Zhao et al, 2016b). The tricarboxylic (TCA) cycle and several amino acid-related biological pathways were disturbed.…”