3.2.1 Phytotoxicity at Morphological Level
Upon interaction with plants, TiO 2 -NPs significantly influence the morphological characteristics of plants such as seed
germination, growth potential and biomass (Zheng et al.
2005; Raliya et al. 2015a, b; Santos Filho et al. 2019). An
extensive research revealed that TiO 2 -NPs show both beneficial and detrimental effects on seed germination and
growth (Andersen et al. 2016). However, there are some
studies reported no significant impacts on seed germination
or growth parameters in plant like Lactuca sativa, Brassica
campestris, Phaseolus vulgaris (Song et al. 2013), Solanum
lycopersicum (Raliya et al. 2015b), Zea mays (Asli and
Neumann 2009) and Hordeum vulgare (Mattiello et al.
2015). Andersen et al. (2016) also reported seed germination, root elongation and growth in plant species varying
from one species to other. Results showed that TiO 2 -NPs can
penetrate the seed coat and accumulate within tissues, but it
did not show toxicity. Studies reported that TiO 2 -NPs at its
optimal concentration showed positive impacts on root and
shoot growth of the Triticum aestivum. The biomass as well
as dry weight of the root was also extremely affected by
TiO 2 -NPs (Feizi et al. 2012; Mahmoodzadeh and Aghili
2014). In a study, Zheng et al. (2005) observed positive
impacts of TiO 2 -NPs on seed germination rate, germination
index, seed vigor index and seedling growth of spinach.
Similar results for these parameters for TiO 2 -NPs were also
reported in several plant species, including Spinacia oleracea (Zheng et al. 2005; Yang et al. 2007), cucumber
(Servin et al. 2012), Agropyron desertorum (Azimi et al.
2013), Foeniculum vulgare (Feizi et al. 2013), Brassica
napus (Mahmoodzadeh et al. 2013), Solanum lycopersicum
(Raliya et al. 2015b), Arabiodpis thaliana (Tumburu et al.
2015), Linum usitatissimum (Aghdam et al. 2016),Vigna
radiata (Singh et al. 2016), Hordeum vulgare (Janmohammadi et al. 2016) and Arachis hypogaea (Rui et al. 2018).
According to them, TiO 2 -NPs’ treatment improves seed
performance and various morphological parameters such as
root elongation, shoot growth, seedling growth, number of
lateral roots, leaf area and plant biomass. TiO 2 -NPs mediate
photo-generation of superoxide and hydroxide anions and
can reactivate the aged seeds. Besides they may enhance
penetrability of the seed capsule and induce oxidation–reduction reactions that would improve the water and oxygen
imbibition in seeds, and thus accelerate the metabolism and
promote seed germination (Zheng et al. 2005; Azimi et al.
2013).
Raliya et al. (2015b) found that differences in TiO 2 -NPs
treatments (through foliar and soil amendment) showed
contrasting effects on root length. They reported that foliar
treatments of TiO 2 -NPs significantly reduce the root length
Table 2 (continued)
S. No. Plants
Application of TiO 2 -NPs
Concentrations
Impacts
References
6
Zea mays
<100 nm,mixture (rutile and
anatase), seeds soaked
0.2, 1.0, 2.0, and
4.0‰
Damaged structure of DNA, reduction in
mitotic index
Castiglione
et al. (2011)
7
Vician
arbonensis
<100 nm,mixture (rutile and
anatase), seeds soaked
0.2, 1.0, 2.0, and
4.0‰
Chromosomal structure fragmentations
and damage
Castiglione
et al. (2011)
8
Cucurbita
pepo
23–31 nm, mixture (rutile and
anatase), suspended in media
50 mg l
−1
Damaged genomic DNA
Moreno-Olivas
et al. (2014)
IV
Yields and productivity
1
Solanum
lycopersicum
22–28.5 nm, anatase, soil and
foliar application
0–1000 mg kg
−1
Enhanced fruit yields, biomass and
productivity
Raliya et al.
(2015b)
2
Linum
usitatissimum
10–25 nm, anatase, foliar
application
0, 10, 100 and
500 mg l
−1
Enhanced seed oil, yield and protein
contents
Aghdam et al.
(2016)
3
Arachis
hypogaea
5 nm,anatase, NP powders
blended with soil mixture
50 and
500 mg kg
−1
Promoted crop yield and its nutritional
quality
Rui et al. (2018)
4
Hordeum
vulgare
foliar application of nTiO 2
using spray
0 and 2000 ppm
Increased grain yield and biomass
Janmohammadi
et al. (2016)
5
Triticum
aestivum
foliar application of nTiO 2
using spray
0.01%, 0.02%,
0.03%
Enhanced plant growth, yield and quality
(gluten and starch content)
Jaberzadeh et al.
(2013)
6
Spinacia
oleracea
5 nm, anatase, seeds soaked
and foliar application
0.25%
Enhanced biomass, nutritional quality and
improved yield
Yang et al.
(2007)
7
Spinacia
oleracea
Rutile, seeds soaked in
TiO 2- NPs solution
0, 0.25, 0.5, 1.0,
1.5, 2.0, 2.5, 4.0,
6.0%
Improved biomass and yield
Zheng et al.
(2005)
8
Oryza sativa
20 nm, anatase, suspended in
Hoagland nutrient solution
0, 100, 250, and
500 mg l
−1
Reduction in biomass
Wu et al. (2017)
58
R. Singh et al.
Upon interaction with plants, TiO 2 -NPs significantly influence the morphological characteristics of plants such as seed
germination, growth potential and biomass (Zheng et al.
2005; Raliya et al. 2015a, b; Santos Filho et al. 2019). An
extensive research revealed that TiO 2 -NPs show both beneficial and detrimental effects on seed germination and
growth (Andersen et al. 2016). However, there are some
studies reported no significant impacts on seed germination
or growth parameters in plant like Lactuca sativa, Brassica
campestris, Phaseolus vulgaris (Song et al. 2013), Solanum
lycopersicum (Raliya et al. 2015b), Zea mays (Asli and
Neumann 2009) and Hordeum vulgare (Mattiello et al.
2015). Andersen et al. (2016) also reported seed germination, root elongation and growth in plant species varying
from one species to other. Results showed that TiO 2 -NPs can
penetrate the seed coat and accumulate within tissues, but it
did not show toxicity. Studies reported that TiO 2 -NPs at its
optimal concentration showed positive impacts on root and
shoot growth of the Triticum aestivum. The biomass as well
as dry weight of the root was also extremely affected by
TiO 2 -NPs (Feizi et al. 2012; Mahmoodzadeh and Aghili
2014). In a study, Zheng et al. (2005) observed positive
impacts of TiO 2 -NPs on seed germination rate, germination
index, seed vigor index and seedling growth of spinach.
Similar results for these parameters for TiO 2 -NPs were also
reported in several plant species, including Spinacia oleracea (Zheng et al. 2005; Yang et al. 2007), cucumber
(Servin et al. 2012), Agropyron desertorum (Azimi et al.
2013), Foeniculum vulgare (Feizi et al. 2013), Brassica
napus (Mahmoodzadeh et al. 2013), Solanum lycopersicum
(Raliya et al. 2015b), Arabiodpis thaliana (Tumburu et al.
2015), Linum usitatissimum (Aghdam et al. 2016),Vigna
radiata (Singh et al. 2016), Hordeum vulgare (Janmohammadi et al. 2016) and Arachis hypogaea (Rui et al. 2018).
According to them, TiO 2 -NPs’ treatment improves seed
performance and various morphological parameters such as
root elongation, shoot growth, seedling growth, number of
lateral roots, leaf area and plant biomass. TiO 2 -NPs mediate
photo-generation of superoxide and hydroxide anions and
can reactivate the aged seeds. Besides they may enhance
penetrability of the seed capsule and induce oxidation–reduction reactions that would improve the water and oxygen
imbibition in seeds, and thus accelerate the metabolism and
promote seed germination (Zheng et al. 2005; Azimi et al.
2013).
Raliya et al. (2015b) found that differences in TiO 2 -NPs
treatments (through foliar and soil amendment) showed
contrasting effects on root length. They reported that foliar
treatments of TiO 2 -NPs significantly reduce the root length
Table 2 (continued)
S. No. Plants
Application of TiO 2 -NPs
Concentrations
Impacts
References
6
Zea mays
<100 nm,mixture (rutile and
anatase), seeds soaked
0.2, 1.0, 2.0, and
4.0‰
Damaged structure of DNA, reduction in
mitotic index
Castiglione
et al. (2011)
7
Vician
arbonensis
<100 nm,mixture (rutile and
anatase), seeds soaked
0.2, 1.0, 2.0, and
4.0‰
Chromosomal structure fragmentations
and damage
Castiglione
et al. (2011)
8
Cucurbita
pepo
23–31 nm, mixture (rutile and
anatase), suspended in media
50 mg l
−1
Damaged genomic DNA
Moreno-Olivas
et al. (2014)
IV
Yields and productivity
1
Solanum
lycopersicum
22–28.5 nm, anatase, soil and
foliar application
0–1000 mg kg
−1
Enhanced fruit yields, biomass and
productivity
Raliya et al.
(2015b)
2
Linum
usitatissimum
10–25 nm, anatase, foliar
application
0, 10, 100 and
500 mg l
−1
Enhanced seed oil, yield and protein
contents
Aghdam et al.
(2016)
3
Arachis
hypogaea
5 nm,anatase, NP powders
blended with soil mixture
50 and
500 mg kg
−1
Promoted crop yield and its nutritional
quality
Rui et al. (2018)
4
Hordeum
vulgare
foliar application of nTiO 2
using spray
0 and 2000 ppm
Increased grain yield and biomass
Janmohammadi
et al. (2016)
5
Triticum
aestivum
foliar application of nTiO 2
using spray
0.01%, 0.02%,
0.03%
Enhanced plant growth, yield and quality
(gluten and starch content)
Jaberzadeh et al.
(2013)
6
Spinacia
oleracea
5 nm, anatase, seeds soaked
and foliar application
0.25%
Enhanced biomass, nutritional quality and
improved yield
Yang et al.
(2007)
7
Spinacia
oleracea
Rutile, seeds soaked in
TiO 2- NPs solution
0, 0.25, 0.5, 1.0,
1.5, 2.0, 2.5, 4.0,
6.0%
Improved biomass and yield
Zheng et al.
(2005)
8
Oryza sativa
20 nm, anatase, suspended in
Hoagland nutrient solution
0, 100, 250, and
500 mg l
−1
Reduction in biomass
Wu et al. (2017)
58
R. Singh et al.