different water levels. The results showed that NP application improved the wheat plant growth and photosynthesis,
reduced the Cd levels in wheat grains and the oxidative
stress in leaves. The different parameters like hydrogen
peroxide production, leakage of electrolytes and malondialdehyde were reduced and superoxide dismutase and peroxidase activities by NPs application on wheat plants. The
test NPs improved in wheat plant growth and reduced
oxidative stress and Cd in tissues in dosage-dependent
manner (Khan et al. 2020a, b).
The study by Zhang et al. (2018) examined the effect of
nCu exposure on the root morphology, physiology and gene
transcription levels of wheat (T. aestivum L.). The results
showed decrease in relative growth rate of roots and the
formation of lateral roots. The nitrogen uptake was
increased, and auxin was accumulated in lateral roots of test
plants. The antioxidant (proline) was induced that scavenged
excess reactive oxygen species and alleviation of Cu phytotoxicity (Zhang et al. 2018). In a study by Rico et al.
(2020), two generations of wheat plants were exposed to low
or high nitrogen soil amended with CeO 2 -NPs. The results of
NP treatment showed change in DNA/RNA metabolites, i.e.,
thymidine, uracil, guanosine, deoxyguanosine, adenosine
monophosphate in test plants. The wheat grains exhibited
decrease in Fe concentration by 13–16% (Rico et al. 2020).
The mesoporous silica nanoparticles (MSNs) effects were
evaluated in wheat and lupin plants by Sun et al. (2016) for
the growth and development. The results of NP application
increased rate of germination and plant biomass. The growth
of test plants was accompanied with enhanced total protein,
chlorophyll and rate of photosynthesis was increased (Sun
et al. 2016). The study of wheat (T. aestivum L.) in a
greenhouse under drought and non-drought conditions was
evaluated by use of urea coated with ZnO-NPs or bulk ZnO
by Dimkpa et al. (2020a, b). The drought treatment and NP
application on wheat plants affected parameters like time of
panicle initiation was increased, grain yield reduced, and
uptake of Zn, nitrogen (N), and phosphorus (P) was inhibited. The drought-treated plants with ZnO-NPs reduced
panicle initiation, and bulk ZnO showed no effect on panicle
initiation. The NPs coated urea increased grain yield by 51%
and uncoated urea enhanced to 39%. The coated ZnO-NPs
increased Zn uptake to 24% in plants and 8% with uncoated
ZnO. The coated bulk ZnO applied to test plants enhanced
Zn uptake to 78% and uncoated increased to 10%. The Zn
treatment to plants of without drought showed no change in
time for panicle initiation. The findings demonstrated that
NPs coated urea increases the performance of treated plants
and accumulation of Zn. This study suggested application of
nanoscale micronutrients as an approach for better crop yield
(Dimkpa et al. 2020a, b).
3 Engineered nanoparticles as fertilizers
in different plants
The factorial-based randomized design was applied to study
the morphology and biochemistry of basil (Ocimum basilicum L.) plants by Abbasifar et al. (2020) through treatment
with Zn and Cu-NPs. The results of nutrient treatments
(4000 ppm) Zn-NPs and (2000 ppm) Cu-NPs improved the
plant morphology. The leaves of treated basil plants showed
increase in chlorophyll-a, b, total chlorophyll and carotenoid. The total phenolic and flavonoid content and
antioxidant activity was improved by test NPs. The foliar
application of the Zn and Cu-NPs improved the quantity and
quality in basil (Abbasifar et al. 2020).
Linares et al. (2020) investigated the seedlings growth of
Hordeum vulgare in soil with AgNPs. The shoot and root
tissues of barley were evaluated for Ag bioconcentration and
distribution after exposure to test NPs. The bioconcentration
values of Ag were high in the plants grown in soil from
OECD than the Delacour. The morphological changes in
barley seedlings were small shoots and short, thick roots
after exposure to NPs. It was concluded that early diagnosis
of test NP exposure was plant structural responses in seedlings in biosolid-amended soils (Linares et al. 2020).
A study on the application of bulk and nanoparticles—zinc
oxide, titanium oxide and silver on chilli seeds cv. PKM 1 by
using template-free aqueous solution was performed by Kumar
et al. (2020). The nanoparticles effects were analyzed by
parameters like electrical conductivity, antioxidant enzymes,
i.e., catalase and lipid peroxidase, germination (%), shoot, root
length and seedling vigor. The results of 1000 mg kg
−1
ZnO-NPs treated chilli seeds showed the increase in germination and seedling vigor (Kumar et al. 2020).
Kubavat et al. (2020) performed a study based on
chitosan-nanoparticle (CN) prepared and incorporated with
potassium (CNK) to tested pot trials of Zea mays plant. The
different doses of K-formulation were investigated on
NP-treated maize plants. The accumulation was increased in
fresh (51%) and dry biomass (47%) in amended soils with
reduced potassium rates (75% CNK). The CNK improved
root growth by enhancing porosity, water conductivity and
friability of soil. The nano-formulation and the treatment
showed no deleterious effects on test plant but improved
carbon-cycling activity (Kubavat et al. 2020). The composites of microcrystalline cellulose, chitosan and alginate
biopolymers along with ZnO nanoparticles were tested by
Martins et al. (2020) for their potential for controlled release
of Zn. The study was reported by growing the maize plants
in four agriculture soils with distinct pH and organic matter.
The conventional Zn salts applied was leached from the soil,
and Zn was less labile for ZnO-NPs. The ZnO-biopolymers
Plant Physiological Responses to Engineered Nanoparticles
93
reduced the Cd levels in wheat grains and the oxidative
stress in leaves. The different parameters like hydrogen
peroxide production, leakage of electrolytes and malondialdehyde were reduced and superoxide dismutase and peroxidase activities by NPs application on wheat plants. The
test NPs improved in wheat plant growth and reduced
oxidative stress and Cd in tissues in dosage-dependent
manner (Khan et al. 2020a, b).
The study by Zhang et al. (2018) examined the effect of
nCu exposure on the root morphology, physiology and gene
transcription levels of wheat (T. aestivum L.). The results
showed decrease in relative growth rate of roots and the
formation of lateral roots. The nitrogen uptake was
increased, and auxin was accumulated in lateral roots of test
plants. The antioxidant (proline) was induced that scavenged
excess reactive oxygen species and alleviation of Cu phytotoxicity (Zhang et al. 2018). In a study by Rico et al.
(2020), two generations of wheat plants were exposed to low
or high nitrogen soil amended with CeO 2 -NPs. The results of
NP treatment showed change in DNA/RNA metabolites, i.e.,
thymidine, uracil, guanosine, deoxyguanosine, adenosine
monophosphate in test plants. The wheat grains exhibited
decrease in Fe concentration by 13–16% (Rico et al. 2020).
The mesoporous silica nanoparticles (MSNs) effects were
evaluated in wheat and lupin plants by Sun et al. (2016) for
the growth and development. The results of NP application
increased rate of germination and plant biomass. The growth
of test plants was accompanied with enhanced total protein,
chlorophyll and rate of photosynthesis was increased (Sun
et al. 2016). The study of wheat (T. aestivum L.) in a
greenhouse under drought and non-drought conditions was
evaluated by use of urea coated with ZnO-NPs or bulk ZnO
by Dimkpa et al. (2020a, b). The drought treatment and NP
application on wheat plants affected parameters like time of
panicle initiation was increased, grain yield reduced, and
uptake of Zn, nitrogen (N), and phosphorus (P) was inhibited. The drought-treated plants with ZnO-NPs reduced
panicle initiation, and bulk ZnO showed no effect on panicle
initiation. The NPs coated urea increased grain yield by 51%
and uncoated urea enhanced to 39%. The coated ZnO-NPs
increased Zn uptake to 24% in plants and 8% with uncoated
ZnO. The coated bulk ZnO applied to test plants enhanced
Zn uptake to 78% and uncoated increased to 10%. The Zn
treatment to plants of without drought showed no change in
time for panicle initiation. The findings demonstrated that
NPs coated urea increases the performance of treated plants
and accumulation of Zn. This study suggested application of
nanoscale micronutrients as an approach for better crop yield
(Dimkpa et al. 2020a, b).
3 Engineered nanoparticles as fertilizers
in different plants
The factorial-based randomized design was applied to study
the morphology and biochemistry of basil (Ocimum basilicum L.) plants by Abbasifar et al. (2020) through treatment
with Zn and Cu-NPs. The results of nutrient treatments
(4000 ppm) Zn-NPs and (2000 ppm) Cu-NPs improved the
plant morphology. The leaves of treated basil plants showed
increase in chlorophyll-a, b, total chlorophyll and carotenoid. The total phenolic and flavonoid content and
antioxidant activity was improved by test NPs. The foliar
application of the Zn and Cu-NPs improved the quantity and
quality in basil (Abbasifar et al. 2020).
Linares et al. (2020) investigated the seedlings growth of
Hordeum vulgare in soil with AgNPs. The shoot and root
tissues of barley were evaluated for Ag bioconcentration and
distribution after exposure to test NPs. The bioconcentration
values of Ag were high in the plants grown in soil from
OECD than the Delacour. The morphological changes in
barley seedlings were small shoots and short, thick roots
after exposure to NPs. It was concluded that early diagnosis
of test NP exposure was plant structural responses in seedlings in biosolid-amended soils (Linares et al. 2020).
A study on the application of bulk and nanoparticles—zinc
oxide, titanium oxide and silver on chilli seeds cv. PKM 1 by
using template-free aqueous solution was performed by Kumar
et al. (2020). The nanoparticles effects were analyzed by
parameters like electrical conductivity, antioxidant enzymes,
i.e., catalase and lipid peroxidase, germination (%), shoot, root
length and seedling vigor. The results of 1000 mg kg
−1
ZnO-NPs treated chilli seeds showed the increase in germination and seedling vigor (Kumar et al. 2020).
Kubavat et al. (2020) performed a study based on
chitosan-nanoparticle (CN) prepared and incorporated with
potassium (CNK) to tested pot trials of Zea mays plant. The
different doses of K-formulation were investigated on
NP-treated maize plants. The accumulation was increased in
fresh (51%) and dry biomass (47%) in amended soils with
reduced potassium rates (75% CNK). The CNK improved
root growth by enhancing porosity, water conductivity and
friability of soil. The nano-formulation and the treatment
showed no deleterious effects on test plant but improved
carbon-cycling activity (Kubavat et al. 2020). The composites of microcrystalline cellulose, chitosan and alginate
biopolymers along with ZnO nanoparticles were tested by
Martins et al. (2020) for their potential for controlled release
of Zn. The study was reported by growing the maize plants
in four agriculture soils with distinct pH and organic matter.
The conventional Zn salts applied was leached from the soil,
and Zn was less labile for ZnO-NPs. The ZnO-biopolymers
Plant Physiological Responses to Engineered Nanoparticles
93