Responses of seed germination and shoot metabolic profiles of maize (Zea mays L.) to Y(2)O(3) nanoparticle stress

The potential risks of rare-earth nanoparticles (RENPs) to plants in the environment are attracting increasing attention due to their wide-spread application. In this regard, little is known about the effects of Y(2)O(3) NPs as an important member of RENPs on crop plants. Seed germination is vulnerable to environmental stress, which determines the growth and yield of crops. Here, maize seeds were exposed to a Y(2)O(3) NP suspension (0–500 mg L(−1)) in the dark for 6 days. It was found that the Y(2)O(3) NPs had no significant effect on the germination rates (>93%) in all treatments, but they could reduce seed vitality, delay germination, and inhibit seedling growth in a dose-dependent manner. Further, the inhibition effect of Y(2)O(3) NPs on root elongation was much stronger than that on shoot elongation. Meanwhile, the activities of peroxidase (POD) and catalase (CAT) in shoots were enhanced with the increase in the Y(2)O(3) NP concentration. A high-concentration (≥300 mg L(−1)) of Y(2)O(3) NPs induced a significant increase in the malondialdehyde (MDA) level in shoots compared to the control, indicating that the membrane lipid peroxidation and permeability were enhanced. (1)H NMR-based analysis showed that the polar metabolic profiles were altered significantly after treatment with 0, 10, and 500 mg L(−1) of Y(2)O(3) NPs, but there was no marked alteration observed for the non-polar metabolic profiles. The polar metabolites (e.g., sugars, amino acids, and most organic acids) showed a dose-dependent increase to Y(2)O(3) NP stress, indicating that the metabolic pathways of carbohydrate metabolism, the tricarboxylic acid cycle (TCA), and amino acid synthesis were disturbed. There were significantly positive correlations found among the metabolites related with the antioxidant response and osmotic adjustment. The simultaneous accumulation of these metabolites possibly indicated the adaptation of the seedlings to stress at the cost of retarding glycolysis, TCA, and protein synthesis. The retarded effects finally inhibited the apparent growth of the seedlings. These findings reveal the phytotoxicity of Y(2)O(3) NPs and provide physiological and biochemical and molecular-scale perspectives on the response of seedlings to stress.