Agriculture Reference
In-Depth Information
The entry of nanoparticles through the cell wall depends on the pore diameter of
the cell wall (5-20 nm) (Fleischer et al.
1999
). Hence, nanoparticles or nanoparticle
aggregates with diameter less than the pore size of plant cell wall could easily enter
through the cell wall and reach up to the plasma membrane (Moore
2006
; Navarro
et al.
2008
). Functionalized nanoparticles facilitate the enlargement of pore size or
induction of new cell wall pore to enhance the uptake of nanoparticles. Several
reports have discussed the uptake of nanoparticles into plant cell via binding to
carrier proteins through aquaporin, ion channels, or endocytosis (Nair et al.
2010
).
Further, nanoparticles can also be transported into the plant by forming complexes
with membrane transporters or root exudates (Kurepa et al.
2010
). Various other
studies reported that nanoparticles could enter through stomata or the base of
trichome in leaf (Eichert et al.
2008
; Fern´ndez and Eichert
2009
; Uzu
et al.
2010
). Kurepa et al. (
2010
) reported uptake and translocation of TiO
2
-alizarin
red S complex in
Arabidopsis thaliana
seedling. They observed that mucilage
released by roots develops pectin hydrogel complex around the root and found to
be responsible for the entry of nanoparticle-dye complex. In a recent study carried
out to understand the mechanism of nanoparticle uptake and translocation, fluores-
cently labeled monodispersed mesoporous silica nanoparticles were found to pen-
etrate the roots via symplastic and apoplastic pathways and translocated via xylem
tissue to the aerial parts of the plants including the stems and leaves (Sun
et al.
2014
). However, the exact mechanism of nanoparticle uptake by plants is
yet to be elucidated.
After entering the cell, nanoparticles can transport apoplastically or
symplastically. They may be transported via plasmodesmata from one cell to the
other (Rico et al.
2011
). In the cytoplasm, nanoparticles approach to different
cytoplasmic organelles and interfere with different metabolic processes of the cell
(Moore
2006
). Furthermore, Larue et al. (
2011
) studied the uptake of TiO
2
nanoparticles in wheat and observed the nanoparticles in parenchyma and vascular
tissues of the root.
Lin and Xing (
2008
) examined the cell internalization and upward translocation
of ZnO nanoparticles in
Lolium perenne
(ryegrass). They showed that ZnO
nanoparticles could enter the ryegrass root cells and move up to the vascular tissues.
L
opez-Moreno et al. (
2010
) studied the uptake and accumulation of ZnO
nanoparticles in
G. max
seedling. They treated the seeds with ZnO nanoparticles
in the concentration of 500-4,000 ppm and reported higher Zn uptake at 500 ppm.
They proposed that at higher concentration nanoparticles get agglomerated which
inhibits the nanoparticles entry into the seed through cell wall pores. Moreover,
X-ray absorption spectroscopy of ZnO-treated seedlings revealed presence of Zn
2+
ions instead of ZnO suggesting the role of roots in ZnO ionization on its surface.
They also showed the presence of ZnO nanoparticles in apoplast, cytoplasm, and
nuclei of the endodermal cell and vascular cylinder by high-magnification trans-
mission electron microscopy.
In case of magnetite nanoparticles, Zhu et al. (
2008
) reported the presence of
nanoparticles in root, stem, and leaves of
Cucurbita maxima
(pumpkin). They
observed that the extent of nanoparticles uptake is affected by the type of growth
