Agriculture Reference
In-Depth Information
In contrast to these abovementioned studies, Mohammadi et al. (
2013
) showed
that treatment of chickpea seeds with low levels of TiO
2
NPs (
10 mg/L) did not
display any negative effect on seed germination and seedling morphology of these
plants. Instead, exposure to TiO
2
NPs strengthened root membrane integrity (e.g.,
lower electrolyte leakage and low membrane lipid oxidation) of both cold-sensitive
and cold-resistant chickpea seedlings during cold treatment. Jaberzadeth
et al. (
2013
) showed that foliar application of low concentrations of TiO
2
NPs to
wheat increased almost all agrometic traits such as plant biomass and yield under
water-deficit stress conditions. Wheat grains exposed to TiO
2
NPs also had higher
gluten and starch content. These studies supported several earlier studies which
showed that foliar treatment of spinach plants with TiO
2
NPs is beneficial for plants
in terms of the overall growth and improvement of plant photosynthesis (Zheng
et al.
2005
). The three principal aspects of photosynthesis that are affected under
foliar treatment with TiO
2
NPs are the light collection aspects of the photochemical
reactions (Hong et al.
2005
; Yang et al.
2007
), the enzyme that initiates the
biochemical reactions (Gao et al.
2006
), and the protection systems that prevent
radicals and lipid peroxidation from inhibiting photosynthesis (Ma et al.
2008
).
Both nano-anatase (4-6 nm mean grain size) and nano-rutile TiO
2
enhanced the
chlorophyll content of sprayed spinach leaves, the capacity to absorb light, the
hydrolysis of water to provide electrons to the photochemical system, and the
activity of the electron transport carriers. Collectively, these effects lead to
increased efficiency in the production of the energy storage compounds (i.e., ATP
and NADPH) needed to drive the synthesis of carbohydrates and other macromol-
ecules. These studies showing the beneficial effect of TiO
2
NPs on photosynthesis,
however, are short-term studies, and TiO
2
NPs were applied only once. Whether
TiO
2
NPs-enhanced photosynthesis after one-time foliar application will be impor-
tant or not in the long term is not known.
<
14.3.4 Phyto-Effect of Cerium Oxide Nanoparticles
Compared with other ENMs, the reported impact of CeO
2
NPs on plants is generally
benign even though anecdotal reports on the toxicity of CeO
2
NPs to plants at very
high concentrations can be spotted in the literature. Ma et al. (
2010a
,
b
) investigated
the potential CeO
2
NP phytotoxicity and found that the seed germination of seven
different species (e.g., radish, canola, tomato, wheat, lettuce, cabbage, cucumber)
was completely unaffected by 2,000 mg/L of CeO
2
NP suspension. Subsequent
investigation showed that root elongation of these plant species was also largely
unaffected. Only lettuce root growth was suppressed by 34 % at this concentration.
Similarly, CeO
2
NPs at 2,000-4,000 mg/L had no overt toxicity on soybean,
although the authors reported genotoxicity as measured by random amplified
polymorphic DNA assay (Lopez-Moreno et al.
2010a
). In a following study, the
same research group reported the effects of 0-4,000 mg/L CeO
2
NP exposure on
alfalfa, corn, cucumber, and lettuce growth (Lopez-Moreno et al.
2010b
).
