The effect of dissolved organic matter (DOM) on nanoparticle toxicity to plants is poorly understood. In this study, tannic acid (TA) was selected as a DOM surrogate to explore the mechanisms of neodymium oxide NPs (Nd2O3 NPs) phytotoxicity to pumpkin (Cucurbita maxima). The results from the tested concentrations showed that 100 mg L−1 Nd2O3 NPs were significantly toxic to pumpkin in term of fresh biomass, and the similar results from the bulk particles and the ionic treatments were also evident. Exposure to 100 mg L−1 of Nd2O3 NPs and BPs in 1/5 strength Hoagland’s solution not only significantly inhibited pumpkin growth, but also decreased the S, Ca, K and Mg levels in plant tissues. However, 60 mg L−1 TA significantly moderated the observed phytotoxicity, decreased Nd accumulation in the roots, and notably restored S, Ca, K and Mg levels in NPs and BPs treated pumpkin. TA at 60 mg L−1 increased superoxide dismutase (SOD) activity in both roots (17.5%) and leaves (42.9%), and catalase (CAT) activity (243.1%) in the roots exposed to Nd2O3 NPs. This finding was confirmed by the observed up-regulation of transcript levels of SOD and CAT in Nd2O3 NPs treated pumpkin analyzed by quantitative reverse transcription polymerase chain reaction. These results suggest that TA alleviates Nd2O3 BPs/NPs toxicity through alteration of the particle surface charge, thus reducing the contact and uptake of NPs by pumpkin. In addition, TA promotes antioxidant enzymatic activity by elevating the transcript levels of genes involved in ROS scavenging. Our results shed light on the mechanisms underlying the influence of DOM on the bioavailability and toxicity of NPs to terrestrial plants.
Keywords: Antioxidant enzyme, dissolved organic matter, gene expression, nutrient distribution
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