bulbs of A. cepa (Fadoju et al. 2020). In a study by Bakshi
et al. (2019), the tomato plants were grown in sewage sludge
amended with nano-TiO 2 in agricultural soil. The NP-treated
plants showed increase in growth parameters like leaf biomass (142%), fruit yield (102%). The test plants were found
with decrease in tannin, lignins of leaf and increase in carbohydrate levels, change in elements like Fe, B, P, Na and
Mn in stem, leaves and changes were less in fruits. The
tomato fruits showed no significant Ti enrichment, and
TiO 2 -NPs proved safe in improving growth and biochemical
parameters (Bakshi et al. 2019).
Further, the study by Noori et al. (2020) investigated
tomato seedlings (Lycopersicon esculentum) for physiological and molecular responses upon exposure to AgNPs and
silver nitrate (AgNO 3 ) in hydroponic media for 7 days. The
results showed 2–7 times decrease in growth rate and
increase in H 2 O 2 and malondialdehyde in exposed plants
than control. There was decrease in enzymatic antioxidant
(50%) and upregulation of genes of ethylene-inducing
xylanase (EIX), peroxidase (POX) and phenylalanine
ammonia-lyase in test plants (Noori et al. 2020).
Improved photosynthesis
The bean (Phaseolus vulgaris L.) plants were sprayed and
applied in soil with CeO 2 -NPs by Salehi et al. (2018). The
results showed absorption of test NPs in dose-dependent
manner; the uptake and translocation by plants was through
both roots and leaves that increased Ce content. The
spraying lowered stomatal density and increased stomatal
length, and alteration in photosynthesis and the electron
transport chain. The increase in Ce content induced accumulation of osmolytes (proline), phytosiderophores (muconate and mugineate) and proteins involved in folding or
turnover. The spray mode of NPs in bean plants was effective compared to soil application (Salehi et al. 2018).
Amelioration of Cd toxicity
The cowpea plants were evaluated by Ogunkunle et al.
(2020) for Cd toxicity after foliar treatment of nano-TiO 2 in
six episodes. The results showed that NPs promoted
parameters in roots and leaves like chlorophyll b, total
chlorophyll content and stress enzymes. The seeds were with
increase in Zn, Mn and Co levels and the roots, shoots and
grains showed decrease in Cd levels in NP-treated plants
after Cd stress. The nano-TiO 2 foliar application proved its
ameliorative potential in cowpea plants for Cd toxicity
(Ogunkunle et al. 2020).
Lian et al. (2020) investigated maize (Zea mays L.) crop
production in Cd-contaminated soils by application of TiO 2 -
NPs. The results showed that root exposure enhanced Cd
uptake and created phytotoxicity in the test plant. The foliar
exposure decreased shoot Cd content and alleviated
Cd-induced toxicity by test NPs through increase in activities of superoxide dismutase (SOD) and glutathione
S-transferase (GST) and upregulation of citrate cycle,
galactose, alanine, aspartate, glutamate, glycine, serine and
threonine metabolism. Sharifan et al. (2020) investigated the
uptake and accumulation of surface charge of ENP cerium
oxide nanoparticles (CeO 2 -NPs) and cadmium (Cd) in the
presence of inorganic phosphorous in soybean seedlings
grown in hydroponic system. The results showed mutual
effect of test NPs and Cd-affected phosphate level in treated
plants.
Increase in seed number
The green pea (Pisum sativum) plants were grown in soil
by Ochoa et al. (2017) amended with nano-CuO, bulk-CuO
(bCuO) and CuCl 2 and indole-3-acetic acid (IAA). The
results showed that NPs reduced the number of plants and
pod biomass by about 50%. The results suggested that the
nutritional quality of test pea pods was improved by use of
nano-CuO and bCuO (Ochoa et al. 2017). The effect on seed
germination and growth performance of pea (P. sativum) by
treatment by poly(vinylpyrrolidone) (PVP) stabilized on
platinum nanoparticles (Pt:PVP) was investigated. The germination rate was decreased, and the other parameters like
dormancy period, arbuscular mycorrhizal fungi and rhizobial
colonization in treated plants were decreased. The results
proved that the average number of seeds was increased to
163.5% and the average seed weight was decreased by
66.7% (Rahman et al. 2020).
Decreased fertilizer use
The greenhouse experiments by Pandorf et al. (2020) were
conducted to study the growth of romaine lettuce (Lactuca
sativa) and nitrate leaching through soil by using 2D graphite carbon nanoparticles (CNPs). Then, the NPs were
combined with fertilizer and the effect on yield, nitrate
leaching and nutrient uptake by lettuce plant was evaluated
by applying in the soil. The results showed that test NP
lowered fertilizer dose and decreased nitrate infiltration
through the soil (Pandorf et al. 2020).
Improved germination
The germination of Vigna radiata was studied by Jung et al.
(2020) of single and binary mixtures of CdO, CuO
nanoparticles under humidity 70–80%. The results showed
the germination rate of bean was high at 80% humidity and
less with single metal NP exposure in both humidity levels.
The metal accumulation rate was high with the nCuO than
nCdO in treated bean plants (Jung et al. 2020). Pariona et al.
90
A. A. H. Khan
et al. (2019), the tomato plants were grown in sewage sludge
amended with nano-TiO 2 in agricultural soil. The NP-treated
plants showed increase in growth parameters like leaf biomass (142%), fruit yield (102%). The test plants were found
with decrease in tannin, lignins of leaf and increase in carbohydrate levels, change in elements like Fe, B, P, Na and
Mn in stem, leaves and changes were less in fruits. The
tomato fruits showed no significant Ti enrichment, and
TiO 2 -NPs proved safe in improving growth and biochemical
parameters (Bakshi et al. 2019).
Further, the study by Noori et al. (2020) investigated
tomato seedlings (Lycopersicon esculentum) for physiological and molecular responses upon exposure to AgNPs and
silver nitrate (AgNO 3 ) in hydroponic media for 7 days. The
results showed 2–7 times decrease in growth rate and
increase in H 2 O 2 and malondialdehyde in exposed plants
than control. There was decrease in enzymatic antioxidant
(50%) and upregulation of genes of ethylene-inducing
xylanase (EIX), peroxidase (POX) and phenylalanine
ammonia-lyase in test plants (Noori et al. 2020).
Improved photosynthesis
The bean (Phaseolus vulgaris L.) plants were sprayed and
applied in soil with CeO 2 -NPs by Salehi et al. (2018). The
results showed absorption of test NPs in dose-dependent
manner; the uptake and translocation by plants was through
both roots and leaves that increased Ce content. The
spraying lowered stomatal density and increased stomatal
length, and alteration in photosynthesis and the electron
transport chain. The increase in Ce content induced accumulation of osmolytes (proline), phytosiderophores (muconate and mugineate) and proteins involved in folding or
turnover. The spray mode of NPs in bean plants was effective compared to soil application (Salehi et al. 2018).
Amelioration of Cd toxicity
The cowpea plants were evaluated by Ogunkunle et al.
(2020) for Cd toxicity after foliar treatment of nano-TiO 2 in
six episodes. The results showed that NPs promoted
parameters in roots and leaves like chlorophyll b, total
chlorophyll content and stress enzymes. The seeds were with
increase in Zn, Mn and Co levels and the roots, shoots and
grains showed decrease in Cd levels in NP-treated plants
after Cd stress. The nano-TiO 2 foliar application proved its
ameliorative potential in cowpea plants for Cd toxicity
(Ogunkunle et al. 2020).
Lian et al. (2020) investigated maize (Zea mays L.) crop
production in Cd-contaminated soils by application of TiO 2 -
NPs. The results showed that root exposure enhanced Cd
uptake and created phytotoxicity in the test plant. The foliar
exposure decreased shoot Cd content and alleviated
Cd-induced toxicity by test NPs through increase in activities of superoxide dismutase (SOD) and glutathione
S-transferase (GST) and upregulation of citrate cycle,
galactose, alanine, aspartate, glutamate, glycine, serine and
threonine metabolism. Sharifan et al. (2020) investigated the
uptake and accumulation of surface charge of ENP cerium
oxide nanoparticles (CeO 2 -NPs) and cadmium (Cd) in the
presence of inorganic phosphorous in soybean seedlings
grown in hydroponic system. The results showed mutual
effect of test NPs and Cd-affected phosphate level in treated
plants.
Increase in seed number
The green pea (Pisum sativum) plants were grown in soil
by Ochoa et al. (2017) amended with nano-CuO, bulk-CuO
(bCuO) and CuCl 2 and indole-3-acetic acid (IAA). The
results showed that NPs reduced the number of plants and
pod biomass by about 50%. The results suggested that the
nutritional quality of test pea pods was improved by use of
nano-CuO and bCuO (Ochoa et al. 2017). The effect on seed
germination and growth performance of pea (P. sativum) by
treatment by poly(vinylpyrrolidone) (PVP) stabilized on
platinum nanoparticles (Pt:PVP) was investigated. The germination rate was decreased, and the other parameters like
dormancy period, arbuscular mycorrhizal fungi and rhizobial
colonization in treated plants were decreased. The results
proved that the average number of seeds was increased to
163.5% and the average seed weight was decreased by
66.7% (Rahman et al. 2020).
Decreased fertilizer use
The greenhouse experiments by Pandorf et al. (2020) were
conducted to study the growth of romaine lettuce (Lactuca
sativa) and nitrate leaching through soil by using 2D graphite carbon nanoparticles (CNPs). Then, the NPs were
combined with fertilizer and the effect on yield, nitrate
leaching and nutrient uptake by lettuce plant was evaluated
by applying in the soil. The results showed that test NP
lowered fertilizer dose and decreased nitrate infiltration
through the soil (Pandorf et al. 2020).
Improved germination
The germination of Vigna radiata was studied by Jung et al.
(2020) of single and binary mixtures of CdO, CuO
nanoparticles under humidity 70–80%. The results showed
the germination rate of bean was high at 80% humidity and
less with single metal NP exposure in both humidity levels.
The metal accumulation rate was high with the nCuO than
nCdO in treated bean plants (Jung et al. 2020). Pariona et al.
90
A. A. H. Khan