Developmental and Reproductive Effects of Iron Oxide Nanoparticles in Arabidopsis thaliana

Abstract

Increasing use of iron oxide nanoparticles in medicine and environmental remediation has led to concerns regarding exposure of these nanoparticles to the public. However, limited studies are available to evaluate their effects on the environment, in particular on plants and food crops. Here, we investigated the effects of positive (PC) and negative (NC) charged iron oxide (Fe₂O₃) nanoparticles (IONPs) on the physiology and reproductive capacity of Arabidopsis thaliana at concentrations of 3 and 25 mg/L. The 3 mg/L treated plants did not show evident effects on seeding and root length. However, the 25 mg/L treatment resulted in reduced seedling (positive-20% and negative-3.6%) and root (positive-48% and negative-negligible) length. Interestingly, treatment with polyethylenimine (PEI; IONP-PC coating) also resulted in reduced root length (39%) but no change was observed with polyacrylic acid (PAA; IONP-NC coating) treatment alone. However, treatment with IONPs at 3 mg/L did lead to an almost 5% increase in aborted pollen, a 2%-6% reduction in pollen viability and up to an 11% reduction in seed yield depending on the number of treatments. Interestingly, the treated plants did not show any observable phenotypic changes in overall size or general plant structure, indicating that environmental nanoparticle contamination could go dangerously unnoticed.

Keywords: Arabidopsis thaliana; iron oxide; nanoparticle; phytotoxicity; plant development; pollen viability; seed yield.

Figure 1

Transmission electron micrograph (TEM) imaging and magnetic moment measurements of iron oxide nanoparticles (IONP) transport in A. thaliana tissues. (a) TEM image of the iron oxide NPs used in this experiment, showing spherical shape; (b) Zeta potential plot of the IONP-NC solution; (c) Magnetic measurements of the root tissues at 24, 48 and 72 h after watering with 30 mL of a 3 mg/L IONP-NC; (d) magnetic measurement of the leaf tissues at 24, 48 and 72 h after watering with 30 mL of a 3 mg/L IONP-NC; (e,f) magnetic moment measurements of IONP-PC and IONP-NC in flowers (e) and seeds (f).

Figure 2

Effect of IONP treatment on overall seedling length in A. thaliana. Mean seedling length of plants grown on agar media containing either IONP-PC (red), IONP-NC (blue), PAA only (green) or PEI only (orange) compared with agar control (gray). A. thaliana Col-0 seeds were grown in MS media supplemented with IONPs at 25 mg/L and PEI or PAA at 12.5 mg/L. Seedling lengths were measured six days after planting. Treatments marked with asterisks were significantly different from the control with p < 0.0001. For all treatments n = 140.

Figure 3

Changes in A. thaliana seedling root length after exposure to IONPs. Seeds were grown in MS media supplemented with either INOP-PC or IONP-NC at concentrations of 3 µg/mL (blue) or 25 µg/mL (red); or PAA only (green) or PEI only (orange) at 12.5 mg/L and compared with growth media only control (gray), Root lengths were measured six days after planting. Treatments with significant difference of p < 0.009 are marked with two asterisks; p < 0.0001 are marked with three asterisks. For all treatments n = 74.

Figure 4

Effects of IONPs on Pollen tube growth in A. thaliana. Plants were treated with 30 mL of a solution containing IONP-PC or IONP-NC at a concentration of 3 mg/L either once (14 dap; gray bars); twice (14 & 21 dap; blue bars) or three times (14, 21 & 28 dap; red bars) and compared with dH₂O only controls. Pollen was then collected from fresh flowers of treated plants and grown on pollen tube germination media for 18 h before pollen tube length was measured. Treatments with significant differences from the control are marked with an asterisk (p < 0.05). For all experiments n = 100.

Figure 5

Treatment of A. thaliana with IONPs results in reduced seed production. A. thaliana Col-0 plants were grown in soil and watered once (14 dap, blue) twice (14 & 21 dap, red) or three times (14, 21 & 28 dap, green) with 30 mL of IONP-PC or IONP-NC at 3 mg/L and compared with dH₂O only controls (gray). For all experiments n = 1200 siliques per treatment. Single asterisks represent treatments that were significantly different from the control with a p < 0.05; two asterisks indicate treatments that were significantly different with a p < 0.01.