Cr NPs showed no effect on the dehydrogenase activity,
while the Ni NPs showed a mixed effect. The Ni NPs with
the small concentration showed a slight increase (9.2%), in
enzyme activity while a concentration of 100 mg kg
−1
caused a significant inhibitory effect (86.9%) on soil dehydrogenase activity. Kim et al. (2011) observed the toxic
effect of Zn NPs on soil dehydrogenase activity which
decreased significantly. Josko et al. (2014) observed that the
effect of the Zn and Cu NPs caused inhibition of the urease
enzyme activity, while Cr and Ni NPs stimulated them. The
inhibition caused by Zn NPs in the soil type SL1 ranged
between 11.7 and 41.6%, while for SL2, it was between 2.1
and 53.7%. Cu NPs ranged between 0.7 and 44% in both
types of soils under experiment. In a study by Luo et al.
(2020), it was found that the activities of different soil
enzymes increased on the interaction of Ce and Cr NPs with
elevated atmospheric CO 2 levels, while their activity was
found to decrease on using the NPs alone. The soil enzymes
tested under these conditions were soil dehydrogenase,
urease, and acid phosphatase. Phosphatase activity is measured in two types, acidic phosphatase, and alkaline phosphatase. The acid phosphatase of the soil was inhibited on
the addition of Zn, Cu, and Cr NPs in soil type SL1 and
Ni NPs in SL2 soil type (Josko et al. 2014). In SL2 soil type,
stimulation of the soil acid phosphatase was observed on the
addition of Zn NPs. In a study by Kim et al. (2011), the acid
phosphatase activity in the soil decreased upon the addition
of different Zn NPs at different concentrations.
In a study by You et al. (2018), the metal oxide NPs were
used, and it concludes that the saline-alkali soils are more
susceptible than the black soil with respect to their enzyme
activities. It also states that the metal oxide NP incubation
significantly influences the soil enzyme activities and even
changes the soil bacterial community. In a study by Peyrot
et al. (2014), it was found that Ag NPs in low concentrations
have a higher toxic effect when compared to their increased
concentration effect. This may be attributed to the role played
by the colloidal form of silver. Multiple factors affect the
activity of enzymes concerned with NPs. The soil enzyme
activity is affected by NP size (such as bulk and nano forms),
the contact time of NPs and soil, type of soil, and the kind of
enzyme. In general, the soil enzyme activity decreases with
the addition of NPs in large concentrations, while a small
amount addition of NPs tends to have a stimulating effect in
some cases. Though this deduction fits in many cases, the
exact effect can be concluded only upon its observation as the
enzyme NP interaction is a multifactor study (Kim et al.
2011). Apart from this, the intracellular enzymes are much
more sensitive than the extracellular enzymes (Asadishad
et al. 2017). This may be due to the adhesion of the extracellular enzymes on the surface of clay particles due to which
the NPs have a hard time coming in contact with enzymes.
4 Uptake and Translocation of Engineered
Nanoparticles in Plants
Interaction of ENPs with plants is dependent on various factors which include species types, transpiration rate, route of
exposure, physicochemical properties, exposure duration, and
size of NPs (Dietz and Herth 2011; Ma et al. 2015; Duran et al.
2017; Kranjc et al. 2018; Noori et al. 2017; Xiong et al. 2017;
Zhao et al. 2017). During agricultural practices, plants are
presumably exposed to ENPs due to nanotechnological
applications like nanopesticides and nanofertilizers, the use of
sewage sludge, and atmospheric depositions (GardeaTorresdey et al. 2014; Xiong et al., 2017). The fate of atmospheric ENPs on leaves are either they are trapped on the
surface by the cuticular wax layer or can enter into the plants
through natural openings like stomata (Fig. 4). However, the
uptake of ENPs from the soil by roots depends on various
factors like cation exchange capacity, pH, rhizospheric exudates, and microorganisms (Du et al. 2017; Huang et al. 2017;
Noori et al. 2017; Xue et al. 2017; Rossi et al. 2018).
Initially, ENPs are accumulated on the surface as roots
secrete mucilage or organic acids which are negatively
Fig. 4 Uptake and translocation
mechanism of engineered
nanoparticles in plants
208
A. Kumar et al.
while the Ni NPs showed a mixed effect. The Ni NPs with
the small concentration showed a slight increase (9.2%), in
enzyme activity while a concentration of 100 mg kg
−1
caused a significant inhibitory effect (86.9%) on soil dehydrogenase activity. Kim et al. (2011) observed the toxic
effect of Zn NPs on soil dehydrogenase activity which
decreased significantly. Josko et al. (2014) observed that the
effect of the Zn and Cu NPs caused inhibition of the urease
enzyme activity, while Cr and Ni NPs stimulated them. The
inhibition caused by Zn NPs in the soil type SL1 ranged
between 11.7 and 41.6%, while for SL2, it was between 2.1
and 53.7%. Cu NPs ranged between 0.7 and 44% in both
types of soils under experiment. In a study by Luo et al.
(2020), it was found that the activities of different soil
enzymes increased on the interaction of Ce and Cr NPs with
elevated atmospheric CO 2 levels, while their activity was
found to decrease on using the NPs alone. The soil enzymes
tested under these conditions were soil dehydrogenase,
urease, and acid phosphatase. Phosphatase activity is measured in two types, acidic phosphatase, and alkaline phosphatase. The acid phosphatase of the soil was inhibited on
the addition of Zn, Cu, and Cr NPs in soil type SL1 and
Ni NPs in SL2 soil type (Josko et al. 2014). In SL2 soil type,
stimulation of the soil acid phosphatase was observed on the
addition of Zn NPs. In a study by Kim et al. (2011), the acid
phosphatase activity in the soil decreased upon the addition
of different Zn NPs at different concentrations.
In a study by You et al. (2018), the metal oxide NPs were
used, and it concludes that the saline-alkali soils are more
susceptible than the black soil with respect to their enzyme
activities. It also states that the metal oxide NP incubation
significantly influences the soil enzyme activities and even
changes the soil bacterial community. In a study by Peyrot
et al. (2014), it was found that Ag NPs in low concentrations
have a higher toxic effect when compared to their increased
concentration effect. This may be attributed to the role played
by the colloidal form of silver. Multiple factors affect the
activity of enzymes concerned with NPs. The soil enzyme
activity is affected by NP size (such as bulk and nano forms),
the contact time of NPs and soil, type of soil, and the kind of
enzyme. In general, the soil enzyme activity decreases with
the addition of NPs in large concentrations, while a small
amount addition of NPs tends to have a stimulating effect in
some cases. Though this deduction fits in many cases, the
exact effect can be concluded only upon its observation as the
enzyme NP interaction is a multifactor study (Kim et al.
2011). Apart from this, the intracellular enzymes are much
more sensitive than the extracellular enzymes (Asadishad
et al. 2017). This may be due to the adhesion of the extracellular enzymes on the surface of clay particles due to which
the NPs have a hard time coming in contact with enzymes.
4 Uptake and Translocation of Engineered
Nanoparticles in Plants
Interaction of ENPs with plants is dependent on various factors which include species types, transpiration rate, route of
exposure, physicochemical properties, exposure duration, and
size of NPs (Dietz and Herth 2011; Ma et al. 2015; Duran et al.
2017; Kranjc et al. 2018; Noori et al. 2017; Xiong et al. 2017;
Zhao et al. 2017). During agricultural practices, plants are
presumably exposed to ENPs due to nanotechnological
applications like nanopesticides and nanofertilizers, the use of
sewage sludge, and atmospheric depositions (GardeaTorresdey et al. 2014; Xiong et al., 2017). The fate of atmospheric ENPs on leaves are either they are trapped on the
surface by the cuticular wax layer or can enter into the plants
through natural openings like stomata (Fig. 4). However, the
uptake of ENPs from the soil by roots depends on various
factors like cation exchange capacity, pH, rhizospheric exudates, and microorganisms (Du et al. 2017; Huang et al. 2017;
Noori et al. 2017; Xue et al. 2017; Rossi et al. 2018).
Initially, ENPs are accumulated on the surface as roots
secrete mucilage or organic acids which are negatively
Fig. 4 Uptake and translocation
mechanism of engineered
nanoparticles in plants
208
A. Kumar et al.