The reported data from various studies suggests that effect of NPs on plant growth
and seed germination depends on their properties and doses. In most cases, the view
is that NPs cause degradation in the quality of crops because, after penetration into
the plant, they decrease the germination rate of seeds, decrease fresh and dry biomass
as well as the length of roots and shoots, and affect the functioning of many
physiological processes. Nanoparticles can affect the time of flowering, fruiting,
senescence, and dormancy (Vernay et al. 2008; Thul and Sarangi 2015) and thereby
impact the overall growth and development of plants. Upon interaction with plants,
NPs can lower the rate of transpiration in Cucurbita pepo treated with AgNPs
(Musante and White 2012) and in Zea mays treated with TiO 2 NP at concentrations
of 30 and 1000 mgÁL
-1 , respectively (Asli and Neumann 2009). AgNPs and ZnONPs
in Z. mays and Brassica oleracea var. capitata were able to reduce the size of
vacuoles, which consequently led to a reduction in the cell turgidity and size of the
cell (Pokhrel and Dubey 2013). Exposure to ZnONPs resulted in a shrinkage of root
tips due to disintegration of cortical, and epidermis cells (Ma et al. 2010). Zhao et al.
(2013) in turn observed the collapsed structure of vacuoles, cortical cells, epidermis,
and roots after treatment with ZnONPs at a concentration of 1000 mgÁL
-1 . Similarly,
C 70 (C(COOH) 2 ) 4 À 8NPs have an adverse effect on root elongation, whereas they
stimulate negative geotropism in A. thaliana roots (Liu et al. 2010). The effect of
silver nanoparticles at a concentration of 0.5 mgÁL
À1 was phytotoxic in O. sativa for
root and shoot biomass, while the increase in concentration also negatively affected
the leaf surface, chlorophyll, and carotenoid content (Nair and Chung 2014).
In the literature, not only the adverse effects of AgNPs on plant vegetative growth
were observed but also the phytostimulatory ones. For instance, in Crocus sativus,
the application of AgNPs, under conditions of flooding, may promote root growth by
blocking ethylene signaling (Rezvani et al. 2012). Some NPs, such as AgNPs, in
adequate doses activate the gene expression involved in cellular events in
Arabidopsis and promote the accumulation of proteins that are related to the cell
cycle, chloroplast biogenesis, and carbohydrate metabolism (Syu et al. 2014).
AgNPs can also enhance root growth of Arabidopsis and Brassica juncea (Syu
et al. 2014; Sharma et al. 2012).
The detrimental impacts of NPs on photosynthesis have been manifested in the
form of net decreases in the rate of photosynthesis, impediment to seedling growth
and enhancement of chlorosis, and defoliation after exposure to TiO 2 NPs (Siddiqui
et al. 2015). In O. sativa seedlings grown in a hydroponic system with CuONPs at
concentration 1000 mgÁL
-1
, photosynthetic rate, transpiration rate, stomatal conductance, maximal quantum yield of PSII photochemistry, and photosynthetic pigment
contents declined, with a complete loss of PSII photochemical quenching (Da Costa
and Sharma 2016). In turn, ZnONPs inhibited the expression of genes involved in
chlorophyll synthesis and photosystem structure (Wang et al. 2016). In another study
on spinach leaves, TiO 2 NPs increase the Hill reaction through enhancing light
absorption in chlorophyll a, electron transfer, and oxygen evolution rate (Hong
et al. 2005; Su et al. 2007; Zheng et al. 2007a, b; Wang et al. 2008; Monica and
Cremonini 2009). Interactions between gold nanoparticles and plants have been
related to the increase in chlorophyll a fluorescence quenching due to enhanced
1 Nanotechnology in Agriculture, the Food Sector, and Remediation: Prospects,. . .
17
and seed germination depends on their properties and doses. In most cases, the view
is that NPs cause degradation in the quality of crops because, after penetration into
the plant, they decrease the germination rate of seeds, decrease fresh and dry biomass
as well as the length of roots and shoots, and affect the functioning of many
physiological processes. Nanoparticles can affect the time of flowering, fruiting,
senescence, and dormancy (Vernay et al. 2008; Thul and Sarangi 2015) and thereby
impact the overall growth and development of plants. Upon interaction with plants,
NPs can lower the rate of transpiration in Cucurbita pepo treated with AgNPs
(Musante and White 2012) and in Zea mays treated with TiO 2 NP at concentrations
of 30 and 1000 mgÁL
-1 , respectively (Asli and Neumann 2009). AgNPs and ZnONPs
in Z. mays and Brassica oleracea var. capitata were able to reduce the size of
vacuoles, which consequently led to a reduction in the cell turgidity and size of the
cell (Pokhrel and Dubey 2013). Exposure to ZnONPs resulted in a shrinkage of root
tips due to disintegration of cortical, and epidermis cells (Ma et al. 2010). Zhao et al.
(2013) in turn observed the collapsed structure of vacuoles, cortical cells, epidermis,
and roots after treatment with ZnONPs at a concentration of 1000 mgÁL
-1 . Similarly,
C 70 (C(COOH) 2 ) 4 À 8NPs have an adverse effect on root elongation, whereas they
stimulate negative geotropism in A. thaliana roots (Liu et al. 2010). The effect of
silver nanoparticles at a concentration of 0.5 mgÁL
À1 was phytotoxic in O. sativa for
root and shoot biomass, while the increase in concentration also negatively affected
the leaf surface, chlorophyll, and carotenoid content (Nair and Chung 2014).
In the literature, not only the adverse effects of AgNPs on plant vegetative growth
were observed but also the phytostimulatory ones. For instance, in Crocus sativus,
the application of AgNPs, under conditions of flooding, may promote root growth by
blocking ethylene signaling (Rezvani et al. 2012). Some NPs, such as AgNPs, in
adequate doses activate the gene expression involved in cellular events in
Arabidopsis and promote the accumulation of proteins that are related to the cell
cycle, chloroplast biogenesis, and carbohydrate metabolism (Syu et al. 2014).
AgNPs can also enhance root growth of Arabidopsis and Brassica juncea (Syu
et al. 2014; Sharma et al. 2012).
The detrimental impacts of NPs on photosynthesis have been manifested in the
form of net decreases in the rate of photosynthesis, impediment to seedling growth
and enhancement of chlorosis, and defoliation after exposure to TiO 2 NPs (Siddiqui
et al. 2015). In O. sativa seedlings grown in a hydroponic system with CuONPs at
concentration 1000 mgÁL
-1
, photosynthetic rate, transpiration rate, stomatal conductance, maximal quantum yield of PSII photochemistry, and photosynthetic pigment
contents declined, with a complete loss of PSII photochemical quenching (Da Costa
and Sharma 2016). In turn, ZnONPs inhibited the expression of genes involved in
chlorophyll synthesis and photosystem structure (Wang et al. 2016). In another study
on spinach leaves, TiO 2 NPs increase the Hill reaction through enhancing light
absorption in chlorophyll a, electron transfer, and oxygen evolution rate (Hong
et al. 2005; Su et al. 2007; Zheng et al. 2007a, b; Wang et al. 2008; Monica and
Cremonini 2009). Interactions between gold nanoparticles and plants have been
related to the increase in chlorophyll a fluorescence quenching due to enhanced
1 Nanotechnology in Agriculture, the Food Sector, and Remediation: Prospects,. . .
17