Agriculture Reference
In-Depth Information
While AgNPs may be generally perceived as toxic due to their antimicrobial
property, recent two studies with nonagricultural crops may strike a positive note on
the applications of AgNPs to agriculture. One study showed that while AgNPs at
high concentrations exerted toxic effect on poplar and
Arabidopsis
growth, at a
narrow concentration range, AgNPs stimulated the growth of these two plant
species as indicated by their higher root elongation rate, transpiration rate, as well
as higher biomass (Wang et al.
2013a
,
b
). Another study, which is probably more
relevant to the agricultural industry, showed that when horseshoe pelargonium was
sprayed with different concentrations of AgNPs and stored in the dark, AgNPs at
20-60 mg/L improved petal longevity of the flower and enhanced the defense
enzyme activities of the flower plant (Hatami and Ghorbanpour
2014
). APX
activity was highest at 40 mg/L AgNP-treated plants; SOD and CAT activities
and chlorophyll content were also higher, demonstrating some potential beneficial
applications of AgNPs in the storage of agricultural products.
14.3.3 Phyto-Effect of Titanium Dioxide Nanoparticles
As with other ENMs, both positive and negative impacts of TiO
2
NPs on plant
development were reported. Frazier et al (
2013
) showed that TiO
2
NPs significantly
inhibited the seed germination rate, root elongation, and biomass accumulation of
tobacco plants and the plant responses to TiO
2
NPs exposure are concentration
dependent. In addition to the impact on plant physiology, very low concentrations
of TiO
2
NPs (0.1 % of TiO
2
) could significantly alter plant RNA (~20-22 nt)
expressions related to plant development regulations and plant tolerance to abiotic
stresses. When wheat plants were planted and grown in soils conditioned with
TiO
2
NPs for 2 months, wheat biomass was reduced by 13 % compared with plants
grown in soil without TiO
2
NPs (Du et al.
2011
). In this study, the authors also
demonstrated that the soil enzyme activities were significantly reduced. Ghosh
et al. (
2010
) reported that TiO
2
NPs caused chromosomal aberrations in onion
cells and damage to the DNAs in both onion and tobacco root cells as revealed
by different DNA fragmentation techniques. The genotoxic effect of TiO
2
NPs
corroborated well with the reduced root elongation. These researchers also detected
increased concentration of MDA in onion roots when treated with 4 mM of
TiO
2
NPs, and they ascribed TiO
2
NPs impact on plant root membrane integrity as
a possible mechanism for TiO
2
NPs genotoxicity and cytotoxicity. Other researchers
also reported adverse effect of TiO
2
NP suspension on corn leaf development and
transpiration, but attributed the toxic effect of TiO
2
NPs to their physical adsorption
on plant root surface and consequently the reduction of hydraulic conductivity due
to the blockage of root cell wall pores (Asli and Neumann
2009
). A further
examination showed that the diameter of maize root cell wall pores was reduced
from 6.6 to 3.0 nm, which could block cell membrane proteins such as signaling
receptors and membrane uptake channels.
