Biological effects of wheat (Triticum vulgare L.) under the influence metal nanoparticles (Fe, Cu, Ni) and their oxides (Fe3O4, CuO, NiO)

In recent decades, the development of nanotechnology has led to the need for a thorough study of ultrafine metal security. It is known that many of ultrafine metals have pro-oxidant and toxic properties. However, no studies have been performed to comprehensively compare of how the metal and metal oxide nanoparticles (NP) affect plants. We first examined complex morphophysiological parameters in wheat ( Triticum vulgare L.) seedlings exposed for 2 days to spherical nanoparticles (NPs) of Fe0 or Fe3O4, Cu0 or CuO, and Ni0 or NiO at 0.0125 to 1.0 M concentrations. Analysis of metric characteristics showed that the sensitivity to Cu0 NP and Ni0 NP was much higher than that to their oxides (CuO, NiO). NiO NP and CuO NP had no lethal effects at all tested concentrations though caused a significant (more than 2-fold) reduction in most of the growth parameters. At low (less than 0.05 M) levels of Fe NP and Fe3O4 NP the seedlings showed a significantly stimulated growth as compared to control. In contrast, the Cu0 NP, CuO NP, Ni0 NP and NiO NP caused toxic effect on growth which increased as the metal level elevated. The analysis showed a high sensitivity of roots, as the first target for the toxic agents, to low metal concentrations. At low Cu0 NP, CuO NP, NiO NP and Ni0 NP levels in the medium, the root growth was 19 times, 7.4 times, 4.8 times and 2.2 times lower as compared to control. Basing on morphological parameters, the nanoparticles were arranged in the following ascending order of their toxicity for growth of the main root and the first leaf in T. vulgare : Fe3O4→Fe0→NiO→CuO→Ni0→Cu0. Analysis of photosynthetic pigments showed that a 2-day exposure to Fe NP and Fe3O4 NP led to generally more positive and stable effects on pigments as compared to copper and nickel. In the presence of less than 0.05 M metal the seedlings were green with a marked stimulation of pigmentation. At the same time, there was the strongest negative effect of the Cu NP on chlorophyll a (22.0-33.0 %), and Ni NP on chlorophyll b (16.0-68.0 %). The influence of CuO toward lower chlorophyll content was dose-dependent: a statistically significant decrease in chlorophyll a was observed at 0.05, 0.1 and 0.5 M (9.0-21.5 %), and in chlorophyll b at 0.0125 and 0025 M (4.0-15.0 %). NiO NP had insignificant inhibitory effect on chlorophylls at 8.7 % decrease. Carotenoids were less sensitive to tested nanoparticles as compared to chlorophylls. Analysis of MDA content in the seedlings showed that nanoparticles influenced lipid peroxidation in the roots rather than in leaves. The effect of MDA accumulation in roots was the most apparent after exposure to some NPs, especially Ni0 NP, Su0 NP and CuO NP which caused MDA increase exceeding control by 17.0 %, 25.0 % and 18.7 %, respectively. The Fe0, Fe3O4 and NiO NPs did not affect the MDA content, whereas Fe3O4 NP reduced the MDA level by 30.0 %. Thus Fe0, Fe3O4, Cu0, CuO, Ni0 and NiO nanoparticles selectively affect cell metabolism and exhibit different biological activity depending on chemical composition and concentrations.