2012; VandeVoort and Arai 2012; Benoit et al. 2013; Rana and Kalaichelvan 2013;
Jampilek and Kralova 2015).
Plants are an important component of most ecosystems on which many environmental pollutants including nanomaterials have an effect. The effect on plants
depends on the properties of nanoparticles (NPs), i.e., size, shape, concentration,
surface coating, reactivity, and most importantly on the dose. The major sources of
contaminants are the soil and air. Soil is also the final sink of NPs, which can pose a
threat to soil microorganisms and plants (Cornelis et al. 2014).
Exposure to NPs has many physiological and biochemical consequences in
plants. Dietz and Herth (2011) determined five models for interaction between
NPs and living organisms: (a) NPs release metal ions in solution, which causes a
chemical effect; (b) hard spherical particles and their aggregates produce mechanical
effects; (c) catalytic effects occur on the surface of NPs; (d) the surface of the NPs
binds with proteins non-covalently or covalently or produces oxidative effects;
(e) NPs change the chemical environment, in particular the pH. Plants uptake NPs
and transport them to aerial parts of the plant where they cause beneficial or adverse
effects (Siddiqui et al. 2015). A number of studies have demonstrated both the
positive and phytotoxic effects of NPs in plants. However, due to the inability to
decipher the mechanism of how NPs work, contradictory results, for instance, a
reduction or increase in chlorophyll content or the inhibition or stimulation of
growth, look set to remain commonplace.
After the uptake of NPs across the cell wall and cell membrane of the root
epidermis, they enter the plant vascular bundle (xylem) and move to the leaves by
long-distance transport. The cell wall, as a porous network of polysaccharide fibers,
acts as a semipermeable barrier which facilitates only the selected particles to pass
through the pores (Lin et al. 2009; Kurepa et al. 2010; Miralles et al. 2012). The
uptake of NPs via pores on the cell membrane is also size-specific (Ma et al. 2010).
As a consequence, regulation of the transport and accumulation of nanoparticles
depend on the differences in hydraulic conductivity and the pore size of the cell wall.
The mechanical presence of AgNPs in intracellular spaces affects the function of
transporter proteins and blocks cell connections. Aggregated AgNPs (Geisler-Lee
et al. 2013) and ZnONPs (Ma et al. 2010) have been found in the cell wall, indicating
blockage of intercellular communication through obstruction in the plasmodesmata.
Thus, mechanical disruption may affect the transport of nutrients and other materials
when they are present in the plasmodesmata and vascular tract (Zhai et al. 2014).
Aquaporins may be also involved in the regulation of uptake of NPs (Abu-Hamdah
et al. 2004). The most important way via which NPs are distributed and translocated
is the xylem, but transport in the reverse direction to the root through the phloem is
also possible, as for example, in the case of the transport of nCuO (20–40 nm) in Zea
mays (Wang et al. 2012b). Foliar uptake of NPs is possible via cuticular and stomatal
routes (Buick et al. 1993). Sizes of !40 nm enable the transfer of hydrophilic
particles through the pores of stomata (Eichert and Goldbach 2008). Moreover,
leaves exposed to NPs accumulated them in the stomata instead of in the xylem
and translocated them to other parts of the plant via the phloem.
16
A. Gorczyca et al.
Jampilek and Kralova 2015).
Plants are an important component of most ecosystems on which many environmental pollutants including nanomaterials have an effect. The effect on plants
depends on the properties of nanoparticles (NPs), i.e., size, shape, concentration,
surface coating, reactivity, and most importantly on the dose. The major sources of
contaminants are the soil and air. Soil is also the final sink of NPs, which can pose a
threat to soil microorganisms and plants (Cornelis et al. 2014).
Exposure to NPs has many physiological and biochemical consequences in
plants. Dietz and Herth (2011) determined five models for interaction between
NPs and living organisms: (a) NPs release metal ions in solution, which causes a
chemical effect; (b) hard spherical particles and their aggregates produce mechanical
effects; (c) catalytic effects occur on the surface of NPs; (d) the surface of the NPs
binds with proteins non-covalently or covalently or produces oxidative effects;
(e) NPs change the chemical environment, in particular the pH. Plants uptake NPs
and transport them to aerial parts of the plant where they cause beneficial or adverse
effects (Siddiqui et al. 2015). A number of studies have demonstrated both the
positive and phytotoxic effects of NPs in plants. However, due to the inability to
decipher the mechanism of how NPs work, contradictory results, for instance, a
reduction or increase in chlorophyll content or the inhibition or stimulation of
growth, look set to remain commonplace.
After the uptake of NPs across the cell wall and cell membrane of the root
epidermis, they enter the plant vascular bundle (xylem) and move to the leaves by
long-distance transport. The cell wall, as a porous network of polysaccharide fibers,
acts as a semipermeable barrier which facilitates only the selected particles to pass
through the pores (Lin et al. 2009; Kurepa et al. 2010; Miralles et al. 2012). The
uptake of NPs via pores on the cell membrane is also size-specific (Ma et al. 2010).
As a consequence, regulation of the transport and accumulation of nanoparticles
depend on the differences in hydraulic conductivity and the pore size of the cell wall.
The mechanical presence of AgNPs in intracellular spaces affects the function of
transporter proteins and blocks cell connections. Aggregated AgNPs (Geisler-Lee
et al. 2013) and ZnONPs (Ma et al. 2010) have been found in the cell wall, indicating
blockage of intercellular communication through obstruction in the plasmodesmata.
Thus, mechanical disruption may affect the transport of nutrients and other materials
when they are present in the plasmodesmata and vascular tract (Zhai et al. 2014).
Aquaporins may be also involved in the regulation of uptake of NPs (Abu-Hamdah
et al. 2004). The most important way via which NPs are distributed and translocated
is the xylem, but transport in the reverse direction to the root through the phloem is
also possible, as for example, in the case of the transport of nCuO (20–40 nm) in Zea
mays (Wang et al. 2012b). Foliar uptake of NPs is possible via cuticular and stomatal
routes (Buick et al. 1993). Sizes of !40 nm enable the transfer of hydrophilic
particles through the pores of stomata (Eichert and Goldbach 2008). Moreover,
leaves exposed to NPs accumulated them in the stomata instead of in the xylem
and translocated them to other parts of the plant via the phloem.
16
A. Gorczyca et al.