Читать книгу Nanotechnology in Plant Growth Promotion and Protection - Группа авторов - Страница 38

Roots of plants can be exposed to TiO₂NPs in both solid substrates such as soils and in liquid substrates where plants were grown hydroponically (Landa et al. 2012; Kořenková et al. 2017; Tan et al. 2017). Nanoparticles generally, and TiO₂NPs specifically tend to adsorb persistently and remain stuck to the root epidermis. Part of the detected TiO₂NPs in roots should always be considered adsorbed to the epidermal cells (Larue et al. 2016). Titanium (Ti) is a naturally occurring element in soils and an increase in Ti root accumulation was observed only in soils contaminated with 125 mg/kg of Ti and above (Tan et al. 2017). When applied on roots, TiO₂NPs were not significantly transported to shoots (Du et al. 2011; Larue et al. 2012a; Larue et al. 2016). Only a few studies are available demonstrating the translocation of TiO₂NPs from root to shoot (Servin et al. 2012, 2013; Larue et al. 2016; Kořenková et al. 2017), however, rutile being preferentially translocated to the leaves (Servin et al. 2012). Even 100 nm TiO₂ nanoparticles have been transferred from roots to leaves in Nicotiana tabacum (Ghosh et al. 2010). It was observed that the rate of TiO₂NPs translocation from roots to shoots is comparatively lower than some other nanomaterials, such as a copper oxide (CuO) and cerium oxide (CeO₂) nanoparticles (Perreault et al. 2014; Barrios et al. 2017). The inhibited translocation may be partially explained by the fact that many cell‐wall pores in plants have a small diameter. Vicia faba was reported to have an average diameter of cell wall pores of 10–14 nm and in some cases up to 20 nm (Hylmö 1955, 1958). Asli and Neumann (2009) reported an average cell wall pore diameter of 6.6 nm for corn (Zea mays). The nanoparticles may be diffused into root tissues through the intercellular spaces without directly entering the cells. Some of the smaller TiO₂NPs may be taken up by endocytosis through root hair (Ovečka et al. 2005).