thermal energy and decrease in electron transport capacity of
PS-II (Tighe-Neira et al. 2018). Increasing the dose of CuO
NPs decreases photosynthetic rate as enzyme RuBP carboxylase gets inactivated; also changes in the rate of transpiration and photosynthetic efficiency of PS-II have higher
impact on plant physiology (Nekrasova et al. 2011; Regier
et al. 2015; Da Costa and Sharma 2016). Similarly, ZnO NPs
have comparable effects on the photosynthetic process
having more negative than positive effects, mainly due to
functional impairments at higher application rates. In summary, the molecular and physiological responses of plants
are linked to ENPs accumulation. Uptake of ENPs can
trigger in vitro or in vivo plant responses subsequently,
either alleviate the nano-toxicity or decrease the ENPs
uptake via different pathways that needs to be studied in
detail.
4.1.3 Effects of Engineered Nanoparticles
on Molecular and Biochemical Properties
of Plants
Molecular and biochemical effects of ENPs help in understanding the mechanism of plant responses. The most
common biochemical effect is an upsurge in the reactive
oxygen species (ROS) upon exposure to ENPs (Panda et al.
2011; Zhao et al. 2012; Speranza et al. 2013; Mukherjee
et al. 2014). ROS plays a key role in signaling reactions in
plants and can cause oxidative damage to plants (Mittler
2017). Various studies showed that excessive ROS results in
alteration in phytohormones, as ROS plays vital role in
hormone perception and transduction (Gechev et al. 2006;
Zhang et al. 2017a, b). Syu et al. (2014) reported that ENPs
exposure could influence gene expression which affects
hormone signaling resulting in change in signaling transduction, and eventually imbalance in phytohormone’s levels.
Metal-based NPs cause oxidative stress in plants by generating ROS. These ENPs trigger the formation of ROS as
they release ions which interact with different groups of
proteins (Gorczyca et al. 2015).
Silver (Ag) NPs treated O. sativa showed excessive ROS
generation which resulted in the upregulation of superoxide
dismutases (SOD) genes viz. FSD, MSD1, and CSD1 genes,
CAT genes, and APXa and APXb genes (Nair and Chung
2014a). This abiotic stress causes an upsurge in ROS generation which eventually results in increased superoxide
dismutase, peroxidases, and catalase enzymes activity (Rui
et al. 2017). Proline was found to be accumulated which
might be a protective mechanism in plants against excessive
ROS to protect the cellular structures (Chiang and Dandekar
1995). Similarly, CeO 2 exposure (0, 100, 500, 1000,
2000 mg kg
−1 ) to L. sativa showed an increase in POD
activity only in roots at 2000 mg kg
−1 , while SOD activities
were enhanced in both roots and shoots at 100 and
500 mg kg
−1 , but decreased at 1000 and 2000 mg kg
−1 .
A significant increase in MDA contents was observed at
1000 and 2000 mg kg
−1 of CeO 2 owing to higher oxidative
stress (Zhang et al. 2017a, b). Conversely, the foliar application of CeO 2 NPs on S. bicolor in drought conditions
increases antioxidant enzyme activities causing lower lipid
peroxidation (Djanaguiraman et al. 2018). CeO 2 NPs imitate
SOD activity and efficiently convert O
2− to H 2 O 2 than SOD
(Heckert et al. 2008). The Ce
4+ and Ce
3+ oxidation states of
CeO 2 NPs lead to redox reactions (Conesa 1995) that
scavenge the ROS produced under drought.
ENP-treated plants exhibit an extensive regulation of
gene and protein, which provide useful information for plant
detoxification or tolerance. Exposure of TiO 2 NPs to T.
aestivum showed no effect on SOD, catalase (CAT), and
glutathione peroxidases (G-POX) activities but decreased the
activities of ascorbate peroxidase (APX), tryptophan
aminotransferase (TAA), and protein content and led to an
alteration in GSH/GSSG ratio.
Graphene oxide NP which is highly used for various
purposes and harms hydrophytes. They are highly mobile in
water bodies such as lakes, rivers and cause negative impact
if released. In addition, these molecules have a toxic effect
on plant physiology such as oxidative stress in mitochondria
(Miralles et al. 2012; Lv et al. 2019). In recent years, ENPs
have achieved special attention as a potential agent for
enhancing crop productivity. TiO 2 and SiO 2 are described to
increase nitrate reductase activity, enhance absorption, and
utilization of water, fertilizers, and antioxidant production
(Peyrot et al. 2014; Xu et al. 2015).
5 Conclusion and Future Perspectives
The invention of different types of ENPs has revolutionized
the field of science and technology. It has been used for
various purposes and as the commercialization of ENPs are
increasing, the risks of health and environmental contamination is an emerging challenge for scientific society. Today,
researchers, industries, and companies are using a wide
range of NPs for research and various other purposes. The
increased production and volume of ENPs raise a potential
concern for the environment and human health. Several
studies reported a wide range of negative effects of ENPs on
viruses, bacteria, plants, and animals. So, it is very crucial to
find out a suitable solution to overcome the negative effects
of NPs and their sustainable use. Thus, it is necessary to
address these issues and open windows for the careful use of
NPs for future applications. Further, there is a need to
explore the knowledge on final fate and impact of NPs in
every different type of contaminated environment and
appropriate guidelines are required to be framed to avoid
contamination. Overall, the future research should be
focused on: (1) to determine the kinetics of ENPs interaction
Impact of Engineered Nanoparticles on Microbial Communities, Soil …
211
PS-II (Tighe-Neira et al. 2018). Increasing the dose of CuO
NPs decreases photosynthetic rate as enzyme RuBP carboxylase gets inactivated; also changes in the rate of transpiration and photosynthetic efficiency of PS-II have higher
impact on plant physiology (Nekrasova et al. 2011; Regier
et al. 2015; Da Costa and Sharma 2016). Similarly, ZnO NPs
have comparable effects on the photosynthetic process
having more negative than positive effects, mainly due to
functional impairments at higher application rates. In summary, the molecular and physiological responses of plants
are linked to ENPs accumulation. Uptake of ENPs can
trigger in vitro or in vivo plant responses subsequently,
either alleviate the nano-toxicity or decrease the ENPs
uptake via different pathways that needs to be studied in
detail.
4.1.3 Effects of Engineered Nanoparticles
on Molecular and Biochemical Properties
of Plants
Molecular and biochemical effects of ENPs help in understanding the mechanism of plant responses. The most
common biochemical effect is an upsurge in the reactive
oxygen species (ROS) upon exposure to ENPs (Panda et al.
2011; Zhao et al. 2012; Speranza et al. 2013; Mukherjee
et al. 2014). ROS plays a key role in signaling reactions in
plants and can cause oxidative damage to plants (Mittler
2017). Various studies showed that excessive ROS results in
alteration in phytohormones, as ROS plays vital role in
hormone perception and transduction (Gechev et al. 2006;
Zhang et al. 2017a, b). Syu et al. (2014) reported that ENPs
exposure could influence gene expression which affects
hormone signaling resulting in change in signaling transduction, and eventually imbalance in phytohormone’s levels.
Metal-based NPs cause oxidative stress in plants by generating ROS. These ENPs trigger the formation of ROS as
they release ions which interact with different groups of
proteins (Gorczyca et al. 2015).
Silver (Ag) NPs treated O. sativa showed excessive ROS
generation which resulted in the upregulation of superoxide
dismutases (SOD) genes viz. FSD, MSD1, and CSD1 genes,
CAT genes, and APXa and APXb genes (Nair and Chung
2014a). This abiotic stress causes an upsurge in ROS generation which eventually results in increased superoxide
dismutase, peroxidases, and catalase enzymes activity (Rui
et al. 2017). Proline was found to be accumulated which
might be a protective mechanism in plants against excessive
ROS to protect the cellular structures (Chiang and Dandekar
1995). Similarly, CeO 2 exposure (0, 100, 500, 1000,
2000 mg kg
−1 ) to L. sativa showed an increase in POD
activity only in roots at 2000 mg kg
−1 , while SOD activities
were enhanced in both roots and shoots at 100 and
500 mg kg
−1 , but decreased at 1000 and 2000 mg kg
−1 .
A significant increase in MDA contents was observed at
1000 and 2000 mg kg
−1 of CeO 2 owing to higher oxidative
stress (Zhang et al. 2017a, b). Conversely, the foliar application of CeO 2 NPs on S. bicolor in drought conditions
increases antioxidant enzyme activities causing lower lipid
peroxidation (Djanaguiraman et al. 2018). CeO 2 NPs imitate
SOD activity and efficiently convert O
2− to H 2 O 2 than SOD
(Heckert et al. 2008). The Ce
4+ and Ce
3+ oxidation states of
CeO 2 NPs lead to redox reactions (Conesa 1995) that
scavenge the ROS produced under drought.
ENP-treated plants exhibit an extensive regulation of
gene and protein, which provide useful information for plant
detoxification or tolerance. Exposure of TiO 2 NPs to T.
aestivum showed no effect on SOD, catalase (CAT), and
glutathione peroxidases (G-POX) activities but decreased the
activities of ascorbate peroxidase (APX), tryptophan
aminotransferase (TAA), and protein content and led to an
alteration in GSH/GSSG ratio.
Graphene oxide NP which is highly used for various
purposes and harms hydrophytes. They are highly mobile in
water bodies such as lakes, rivers and cause negative impact
if released. In addition, these molecules have a toxic effect
on plant physiology such as oxidative stress in mitochondria
(Miralles et al. 2012; Lv et al. 2019). In recent years, ENPs
have achieved special attention as a potential agent for
enhancing crop productivity. TiO 2 and SiO 2 are described to
increase nitrate reductase activity, enhance absorption, and
utilization of water, fertilizers, and antioxidant production
(Peyrot et al. 2014; Xu et al. 2015).
5 Conclusion and Future Perspectives
The invention of different types of ENPs has revolutionized
the field of science and technology. It has been used for
various purposes and as the commercialization of ENPs are
increasing, the risks of health and environmental contamination is an emerging challenge for scientific society. Today,
researchers, industries, and companies are using a wide
range of NPs for research and various other purposes. The
increased production and volume of ENPs raise a potential
concern for the environment and human health. Several
studies reported a wide range of negative effects of ENPs on
viruses, bacteria, plants, and animals. So, it is very crucial to
find out a suitable solution to overcome the negative effects
of NPs and their sustainable use. Thus, it is necessary to
address these issues and open windows for the careful use of
NPs for future applications. Further, there is a need to
explore the knowledge on final fate and impact of NPs in
every different type of contaminated environment and
appropriate guidelines are required to be framed to avoid
contamination. Overall, the future research should be
focused on: (1) to determine the kinetics of ENPs interaction
Impact of Engineered Nanoparticles on Microbial Communities, Soil …
211