Agriculture Reference
In-Depth Information
Fig. 11.9 a
FESEM images of ZnO nanorods, TEM micrographs of
b
an individual ZnO flower
and
c
focused image of a single ZnO nanorod. The upper left and lower right insets in
c
correspond
to the HRTEM image and SAED pattern of a single nanorod, respectively,
d
EDS spectra of ZnO
nanorods. (Adopted with kind permission from Ahmed et al.
2011a
)
The pore diameter of the cell walls having a thickness ranging from 5 to 20 nm,
determines its sieving properties (Fleischer et al.
1999
; Fujino et al.
1998
; Madigan
et al.
2003
; Zemke-White et al.
2000
). Consequently, nanoparticles having a size
smaller than that of the largest pore can easily pass through the cell wall and reach
the plasma membrane. The enlargement of pores or induction of new cell wall pores
might be possible upon interaction with nanoparticles, thus increasing the uptake
of the nanoparticles through the cell wall. For example, ZnO nanoparticles have
been reported to increase permeability and even create “holes” in bacterial cell walls
(Brayner et al.
2006
; Sondi et al.
2004
; Stoimenov et al.
2002
) with pore size similar
to plant cell walls (Carpita et al.
1979
). As the nanoparticles pass the cell wall, they
reach the plasma membrane. This plasma membrane forms a cavity-like structure
which surrounds the nanoparticles and pulls it into the cell during the endocytic pro-
cess. The nanoparticles may also cross the cell membranes using embedded transport
carrier proteins or ion channels. As the nanoparticles enter the cell, they may bind
with different types of organelles (e.g., endoplasmic reticulum, Golgi, and endo-
lysosomal system), and interfere with the metabolic processes at that site, possibly as
a result of the production of reactive oxygen species (ROS) (Jia et al.
2005
).
Plants also get exposed to nanomaterials in atmospheric and terrestrial environ-
ments. Nanomaterials present in air are attached to leaves and other aerial parts
