Using Metabolomics To Investigate The Biological Effects Of Nanomaterials To Plants

Engineering nanomaterials?ENMs?with excellent physical and chemical properties are widely used in various fields,e.g.,energy,electronics,chemical industry,life science,etc.Moreover,ENMs have the potential to be used as nano-fertilizers or nano-pesticides in nano-enabled agriculture.Some NMs with unique physicochemical properties can promote plant photosynthesis and help plant resist biotic and abiotic stresses.Understanding the biological and environmental effects of NMs are important for their safe use.Plants are primary producers of terrestrial ecosystems.NMs taken up by plants might be transferred to human diet through the food chain,posing a risk to human health.Therefore,this study aims to explore the biological effects of ENMs on edible plants.The results will provide guidance for the safe and sustainable application of NMs.In this study,edible plants?cucumber and spinach?were used as model plants.The response of plants to a variety of NMs?Ag NPs,CeO₂ NPs and fullerol?is revealed from phenotypic,physiological,and biochemical level.Meanwhile,GC-MS based metabolomcis were used to elucidate the underlying mechanism of the interaction between NMs and plants.The main findings of this paper are summarized as follows:?1?Ag NPs have a broad spectrum of antibacterial properties,and the prerequisite for their real application is to clarify their biological effects.In this study,4-week-old cucumber plants were foliar exposed to different doses of Ag NPs?0,4 mg and 40mg/plant?and silver ions?0.04 mg and 0.4 mg/plant?for 7 days.The results showed that Ag NPs?4 mg and 40 mg/plant?exhibited toxicity to cucumber leaves in a dose-dependent manner.Silver contents in cucumber leaves exposed to Ag NPs were significantly higher than control.Ag NPs at 40 mg/plant caused visible damages like dehydration and blight on cucumber leaves.Ag NPs at tested doses did not induce a significant reduction in cucumber biomass,while malondialdehyde?MDA?content in leaves significantly increased,suggesting that Ag NPs at 4 and 40 mg/plant caused oxidative stress on cucumber leaves.In addition,268 metabolites were detected by MS-based metabolomics,among which many significantly changed low molecular metabolites were related to antioxidant defense,indicating that Ag NPs exposure activated the antioxidant defense system of plant cells.Furthermore,the analysis of metabolic pathways showed that Ag NPs exposure affected the carbon and nitrogen related metabolites and disturbed the pathways of tricarboxylic acid cycle,alanine metabolism,arginine and proline metabolism.The toxicity of Ag NPs is mainly from silver ions,however,given that some metabolic changes are unique to Ag NPs,the particulate effect of Ag NPs also contributed to the toxicity.?2?CeO₂ NPs with unique enzyme-mimic activity can help plants resist abiotic stress,but their biological effect is not yet clear.In the study,4-week-old spinach plants were foliar exposed to different doses of CeO₂ NPs?0,0.3 and 3 mg/plant?for 3 weeks.Results showed that foliar application of CeO₂ NPs resulted in a significant bioaccumulation of cerium?Ce?in leaves,but Cewas not transferred to the roots.CeO₂NPs exposure had no overt toxic effect on the biomass and chlorophyll content of spinach plant.However,metabolomics analysis showed that both doses of CeO₂ NPs induced significant change in metabolic profile.Low dose of CeO₂ NPs?0.3 mg/plant?induced stronger metabolic changes in spinach leaves as compared to the high dose of CeO₂ NPs?3 mg/plants??low and high dose of CeO₂ NPs induced perturbation of four and one metabolic pathways,respectively?,while high dose of CeO₂ NPs induced stronger metabolic changes than low dose of CeO₂ NPs in roots?low and high dose of CeO₂ NPs induced perturbation of two and eight metabolic pathways,respectively?.?3?Fullerol has excellent performance in quenching free radicals and good biocompatibility.Studying whether fullerol can help plants alleviate abiotic stress will be of great applied value in agriculture.In this study,3-week-old cucumber plant were foliar exposed to Cu SO₄?5 mg/plant??inducer of reactive oxygen radicals?in the presence of fullerol?1 mg and 2 mg fullerol/plant?and absence of fullerol.Results showed that fullerol,an exogenous antioxidant,did not alleviate copper induced oxidative stress.On the contrary,fullerol aggravated the toxic effect of copper ions on plant.The mechnism is that fullerol promoted more copper ions uptaken by plant.Fullerol at both doses had no obvious toxic effect on cucumber plant.In addition,proteomics revealed an interesting result that fullerol exposure triggered the upregulation of proteins related to photosynthesis,such as light-trapping?chlorophyll a/b binding proteins?and electron transport proteins?cytochrome b6/f proteins?in leaves.In summary,Ag NPs at 4 and 40 mg/plant induced toxic effects on cucumber plant,metabolomics could further reveal the underlying mechanism of the toxicity.CeO₂ NPs and fullerol did not induce overt toxicity on plant,however,metabolomics revealed the invisible changes of plant to NPs at the molecular level.These results provided a comprehensive and deep insight into the interactions between ENMs and plants,especially the underlying molecular mechanisms involved in the interactions,which are important for the understanding their environmental and biological risk assessment and NPs'safe and sustainable use.