Agriculture Reference
In-Depth Information
14.4.2 Uptake and Accumulation of Silver Nanoparticles
Stampoulis et al. (
2009
) reported that the uptake of AgNPs by zucchini (
Cucurbita
pepo
) was on average 4.7 times higher in plants exposed to 10-1,000 mg/L of
AgNPs than to their corresponding bulk materials. The authors suggested that
higher dissolution rate of AgNPs than bulk Ag might be responsible for the greater
Ag concentration in AgNPs-treated zucchini. A separate study that involved some
of the same researchers also showed that AgNPs were taken up by soybean roots
and translocated to stems and leaves and the Ag content was two times higher in
AgNPs-treated soybeans than Ag bulk-treated soybeans (Torre-Roche et al.
2013a
).
However, a detailed study on the forms of Ag inside the plants was not evaluated in
both studies. Lee et al. (
2012
) reported that AgNPs as the particulate form were
taken up by both mug bean and sorghum. AgNPs in the plant roots increased with
exposure concentration of AgNPs, but shoot concentration of Ag appeared unaf-
fected by the dosing concentration. They also noticed that growing media played a
significant role in the extent of accumulation of AgNPs by these two species, with
soil greatly reducing the accumulation of AgNPs when compared to agar media.
When AgNPs were exposed to rice seedlings, it was noticed that some AgNPs
deposited on the root surface and some penetrated into plant cells (Mazumdar and
Ahmed
2011
). AgNPs which have successfully penetrated through cell membranes
are predominantly smaller than 25 nm, and the penetration resulted in damaged cell
walls and vacuoles, suggesting that the physical entrance through the cell wall
could be one of the mechanisms for AgNPs internalization. Our previous study with
Arabidopsis
also indicated that there is a size limitation on the potential uptake and
accumulation of AgNPs. In that study, we found that only AgNPs smaller than
40 nm were successfully internalized in
Arabidopsis
root cells and some appeared
to reach the vascular tissues for possible transport to the shoots (Geisler-Lee
et al.
2013
).
Haverkamp and Marshall (
2009
) also investigated the uptake of Ag ion com-
plexes and AgNPs by
Brassica juncea
plants. However, they found no uptake and
accumulation of AgNPs by
Brassica
. Ionic Ag was readily taken up by
Brassica
plant roots, and within plant tissues, ionic Ag was reduced to AgNPs. The reduction
of ionic Ag to zero valent AgNPs in plant tissues appeared common in nature and
provided an opportunity for the biosynthesis of AgNPs (Harris and Bali
2008
). The
biosynthesis of AgNPs is beyond the scope of this chapter, but the literatures on the
biosynthesis of AgNPs suggested that accumulation and storage of AgNPs in plant
tissues may naturally occur and some accumulation of AgNPs in plant tissues may
not necessarily prohibit the application of AgNPs in agricultural practices.
