Agriculture Reference
In-Depth Information
amide, lignin, and carbohydrates were modified by TiO
2
NPs, suggesting that
TiO
2
NPs could affect the metabolic processes of plants.
14.4.4 Uptake and Accumulation of Cerium Oxide
Nanoparticles
Zhang et al. (
2011
) reported that CeO
2
NPs exposed to cucumber hydroponically for
14 days are mostly loosely bound to the root surface and more than 85 % of the NPs
could be washed off with deionized water. Translocation of the particles to shoot
tissue was measurable but insignificant. Smaller nanoparticles (7 nm) were found at
substantially higher amounts than larger particles (25 nm) in plant tissues. Schwabe
et al. (
2013
) also observed some translocation from pumpkin roots to shoots after
8-day exposure to 100 mg/L CeO
2
NPs. However, no cerium was detected in wheat
shoots with similar exposure scenario. Interestingly, the association of cerium with
the roots of both plant species was reduced in the presence of natural organic
matter.
Birbaum et al. (
2010
) were the first to report on CeO
2
NP exposure to terrestrial
plants (corn) under soil conditions. The authors reported that after 14-day exposure
with the CeO
2
NPs in the irrigation water (50 mL of 10
g/mL per day) resulted in
no detection of ceria in the leaves or sap of corn plants. In contrast, Wang
et al. (
2012
) grew tomato from seeds to the maturity of the plants in the presence
of CeO
2
NP-amended (0.1-10 mg/L) irrigation water and reported the detection of
ceria in all plant tissues, including tomato fruits, suggesting translocation. Interest-
ingly, the authors also noticed high concentrations of ceria in tomato seeds irrigated
with 10 mg/L CeO
2
NP-containing solution than controls. The observation that
cerium may cross the phloem membrane and accumulate in fruits was supported
by a recent publication which reported that CeO
2
NPs are bioaccumulated in all
tissues of cucumbers including their roots, stems, leaves, and fruits (Zhao
et al.
2013
). However, the translocation from root to stem only represented a
small fraction of Ce associated with plant roots (1.44 and 1.79 % in plants treated
with 400 and 800 mg/kg CeO
2
NPs). Once ceria has reached the stem tissue, the
upward transport to the leaves became much easier (e.g., 37 % in plants treated with
400 mg/kg of CeO
2
NPs). It was found that CeO
2
NPs were mainly localized in the
vasculature of the leaf vein suggesting that the transport of CeO
2
NPs was with the
water flow. In an earlier study, the authors also demonstrated that the uptake and
accumulation of CeO
2
NPs was heavily affected by the properties of CeO
2
NPs and
the properties of growing media (Zhao et al.
2012
). After 1 month of growth in soil
conditioned with CeO
2
NPs of different surface properties, corn roots accumulated
significantly greater quantities of alginate-coated CeO
2
NPs than uncoated particles.
These authors also noticed that soils with high organic matter generally enhanced
the association of CeO
2
NPs with roots but reduced the translocation to shoots,
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