Metabolic profile and physiological response of cucumber foliar exposed to engineered MoS2 and TiO2 nanoparticles

Nanoparticle (NPs) use is widespread across a wide range of sectors and accurate assessment of risk and/or benefits posed to important receptors such as plant species is necessary to ensure the sustainable development and application of nanotechnology. Here, 4-week old cucumber plants were foliar exposed to different doses (0–27 mg/plant) of MoS2 or TiO2 NPs for 16 d. Foliar NPs exposure had no impact on plant biomass or photosynthetic pigment production. However, the higher dose of TiO2 NPs exposure decreased lipid peroxidation by 34.7%, and the higher dose of MoS2 and TiO2 NPs exposure significantly increased total phenolics content by 27.4%–28.2%. The photosynthetic rate was increased by 23.6–30.8% with exposure to the higher dose of MoS2 NPs, as well as both lower and higher dose of TiO2 NPs. A metabolomic analysis revealed that 33 metabolites were upregulated or downregulated by MoS2 and TiO2 NPs exposure, including 8 amino acids, 5 organic acids, 3 fatty acids, 5 sugar and sugar derivatives, 4 alcohols, and 3 aromatic compounds. The fluctuation in metabolite content suggests that when plants are exposed to NPs, their metabolic processes are altered, and subsequent responses such as modulated defense, adaptation, and photosynthesis are displayed. With regard to dose, the higher concentration of TiO2 NPs altered several metabolic pathways, including carbohydrate and nitrogen metabolism, whereas the lower dose of TiO2 NPs and both doses of MoS2 had minimal impact on cucumber metabolism. These findings suggest that appropriate doses of MoS2 and TiO2 NPs have the potential to increase plant production by increasing plant photosynthetic rate without inducing excessive stress or toxicity. [Display omitted] •Foliar exposure to nanoscale MoS2 at the high dose and TiO2 at both doses increased cucumber photosynthetic rate.•Foliar exposure to the higher TiO2 NPs dose decreased cucumber lipid peroxidation.•Higher dose of TiO2 NPs altered several metabolic pathways, including those involving carbohydrate and nitrogen metabolism.•MoS2 and TiO2 NPs at select doses increased plant production without induced excessive stress or phytotoxicity.