nanoparticles would positively affect growth and growth rate
(Faraji and Sepehri 2018).
5 Studies on the Effect of Nanoparticles
on Germination and Growth of Seedlings
Several studies, some of which are described below, have
been done on the effect of nanoparticles on seedlings in
general and titanium dioxide nanoparticles in particular.
Improvement in the germination of spinach seeds, using
titanium dioxide nanoparticles up to a concentration of
400 µg ml
−1
, was observed, but no improvement when the
higher concentrations were tried (Zhang et al. 2020). An
almost contrary effect was observed (Castiglione et al. 2011)
after seeds of Vicia narbonensis L. and Zea mays L. were
soaked in suspensions of titanium dioxide nanoparticles,
having concentrations up to 4000 µg ml
−1 .
A commercially available source of nanotitanium dioxide
nanoparticles (Evonik P25) was used by Song et al. (2013),
who found that soaking tomato seeds for 24 h in a suspension of the nanoparticles made no noticeable difference in
germination periods. Evonik P25 titanium nanoparticles
were tested by Larue et al. (2011) using a hydroponic
technique, for growing three different seeds. Even after a
7-day treatment under hydroponic conditions, there was no
decrease in germination time.
Based on their assessment that studies described briefly
above were deficient with respect to methodology, Andersen
et al. (2016) resorted to testing the effect of nanoparticles of
TiO 2 and CeO 2 on ten different plant species. These
researchers also used P25 Evonik Degussa on the basis that
they can easily compare their results using the same product.
An important difference was that they passed ultrasound
radiation through the suspensions of the nanoparticles. They
used the seeds of lettuce, cabbage, soybean, carrot, ryegrass,
pineapple cucumber, oat, onion and corn. They sterilized the
seeds with ethanol followed by 50% bleach. They made
some changes to the test procedure whereby they replaced
the sand with Petri dishes and performed the test under
artificial light, to promote possible photocatalytic activity.
They also increased the period over which the changes in
germination were monitored. They did not detect any toxic
effects on germination or growth of the seedlings.
5.1 A Study Involving Transplanting
In the following treatment of seedlings, there are differences
from those described above. Firstly, two-year-old seedlings
of Ulmus elongata were transplanted from one site in China
to another site where the experiment was conducted by Gao
et al. (2013). Secondly, the seeds were not the targets of the
treatment; to wit, the leaves were. The nanoparticles used
were anatase-TiO 2 which was synthesized from TiCl 4 as the
precursor and benzyl alcohol via a sol–gel technique. Each
experiment involved three leaves for spraying with three
different concentrations (0.1, 0.2 and 0.3%) of the
nanoparticle while a 4th leaf, a control, was sprayed with
distilled water. Contrary to results given in the preceding
example, treatment with nanoanatase stunted growth. At
0.4% concentration the leaves began to turn yellow, indicating a lack of chlorophyll. In the light of further experiments, it was concluded that carbohydrates and lipids were
formed under toxicity caused by nanoparticles and that
environmental factors play a very significant role in the
interactions between nanoparticles and plants.
6 Effect of Nano-TiO 2 on Strength of Plants
Whether the structures of plants are strengthened, through
interaction with titanium dioxide nanoparticles, can be
revealed by analysis of the structures after such interactions
have occurred. One study on this aspect was undertaken by
McDaniel et al. (2013). Plants of tobacco, mustard and
jalopeno were grown in potting soil under controlled conditions of temperature, humidity and light. They were then
translocated to a hydroponic solution having a pH of 5.5
where it was left for 3–4 days for acclimatization in a soilless system. Thereafter, the hydroponic solution was
replaced with suspensions of nanotitanium dioxide in water,
containing 0, 75, 150 and 300 mg l
−1 of the nanoparticles.
After 7 days in this suspension, pieces of roots were excised
from the plants, washed with water and treated, in order, as
follows: with glutaraldehyde, osmium tetroxide, dehydrated
with ethanol, dried, coated with gold by sputtering. The
specimens were then analysed by SEM, attached to an
(energy-dispersive X-ray spectroscopy) EDS detector. The
results showed that titanium was detected on all three root
specimens. The mustard root exposed to 300 mg l
−1 had
evidence of damage to epidermal cells whereas the roots of
the same plants exposed to 75 and 150 mg l
−1 showed
growth. On the other hand, the roots of tobacco and jalapeno
did not suffer any damage or experience growth. This may
be taken to indicate that they are hyperaccumulators of TiO 2
or that they did not take up significant amounts of
nanoparticles. In a study involving canola seeds and seedlings, Mahmoodzadeh et al. (2013) treated these seeds to
nanoparticles of titanium dioxide at a very wide range of
concentrations (10, 100, 1000, 1200, 1500, 1700 and
2000 mg l
−1 ). Concentrations of 2000 and 1500 mg l
−1
gave the fastest and slowest germination rates, respectively.
It was also found that the use of uniform size (20 nm mean
size) nanoparticles increased both the rate of germination
and robustness of the seedling.
Interaction of Nano-TiO 2 with Plants: Preparation and Translocation
79
(Faraji and Sepehri 2018).
5 Studies on the Effect of Nanoparticles
on Germination and Growth of Seedlings
Several studies, some of which are described below, have
been done on the effect of nanoparticles on seedlings in
general and titanium dioxide nanoparticles in particular.
Improvement in the germination of spinach seeds, using
titanium dioxide nanoparticles up to a concentration of
400 µg ml
−1
, was observed, but no improvement when the
higher concentrations were tried (Zhang et al. 2020). An
almost contrary effect was observed (Castiglione et al. 2011)
after seeds of Vicia narbonensis L. and Zea mays L. were
soaked in suspensions of titanium dioxide nanoparticles,
having concentrations up to 4000 µg ml
−1 .
A commercially available source of nanotitanium dioxide
nanoparticles (Evonik P25) was used by Song et al. (2013),
who found that soaking tomato seeds for 24 h in a suspension of the nanoparticles made no noticeable difference in
germination periods. Evonik P25 titanium nanoparticles
were tested by Larue et al. (2011) using a hydroponic
technique, for growing three different seeds. Even after a
7-day treatment under hydroponic conditions, there was no
decrease in germination time.
Based on their assessment that studies described briefly
above were deficient with respect to methodology, Andersen
et al. (2016) resorted to testing the effect of nanoparticles of
TiO 2 and CeO 2 on ten different plant species. These
researchers also used P25 Evonik Degussa on the basis that
they can easily compare their results using the same product.
An important difference was that they passed ultrasound
radiation through the suspensions of the nanoparticles. They
used the seeds of lettuce, cabbage, soybean, carrot, ryegrass,
pineapple cucumber, oat, onion and corn. They sterilized the
seeds with ethanol followed by 50% bleach. They made
some changes to the test procedure whereby they replaced
the sand with Petri dishes and performed the test under
artificial light, to promote possible photocatalytic activity.
They also increased the period over which the changes in
germination were monitored. They did not detect any toxic
effects on germination or growth of the seedlings.
5.1 A Study Involving Transplanting
In the following treatment of seedlings, there are differences
from those described above. Firstly, two-year-old seedlings
of Ulmus elongata were transplanted from one site in China
to another site where the experiment was conducted by Gao
et al. (2013). Secondly, the seeds were not the targets of the
treatment; to wit, the leaves were. The nanoparticles used
were anatase-TiO 2 which was synthesized from TiCl 4 as the
precursor and benzyl alcohol via a sol–gel technique. Each
experiment involved three leaves for spraying with three
different concentrations (0.1, 0.2 and 0.3%) of the
nanoparticle while a 4th leaf, a control, was sprayed with
distilled water. Contrary to results given in the preceding
example, treatment with nanoanatase stunted growth. At
0.4% concentration the leaves began to turn yellow, indicating a lack of chlorophyll. In the light of further experiments, it was concluded that carbohydrates and lipids were
formed under toxicity caused by nanoparticles and that
environmental factors play a very significant role in the
interactions between nanoparticles and plants.
6 Effect of Nano-TiO 2 on Strength of Plants
Whether the structures of plants are strengthened, through
interaction with titanium dioxide nanoparticles, can be
revealed by analysis of the structures after such interactions
have occurred. One study on this aspect was undertaken by
McDaniel et al. (2013). Plants of tobacco, mustard and
jalopeno were grown in potting soil under controlled conditions of temperature, humidity and light. They were then
translocated to a hydroponic solution having a pH of 5.5
where it was left for 3–4 days for acclimatization in a soilless system. Thereafter, the hydroponic solution was
replaced with suspensions of nanotitanium dioxide in water,
containing 0, 75, 150 and 300 mg l
−1 of the nanoparticles.
After 7 days in this suspension, pieces of roots were excised
from the plants, washed with water and treated, in order, as
follows: with glutaraldehyde, osmium tetroxide, dehydrated
with ethanol, dried, coated with gold by sputtering. The
specimens were then analysed by SEM, attached to an
(energy-dispersive X-ray spectroscopy) EDS detector. The
results showed that titanium was detected on all three root
specimens. The mustard root exposed to 300 mg l
−1 had
evidence of damage to epidermal cells whereas the roots of
the same plants exposed to 75 and 150 mg l
−1 showed
growth. On the other hand, the roots of tobacco and jalapeno
did not suffer any damage or experience growth. This may
be taken to indicate that they are hyperaccumulators of TiO 2
or that they did not take up significant amounts of
nanoparticles. In a study involving canola seeds and seedlings, Mahmoodzadeh et al. (2013) treated these seeds to
nanoparticles of titanium dioxide at a very wide range of
concentrations (10, 100, 1000, 1200, 1500, 1700 and
2000 mg l
−1 ). Concentrations of 2000 and 1500 mg l
−1
gave the fastest and slowest germination rates, respectively.
It was also found that the use of uniform size (20 nm mean
size) nanoparticles increased both the rate of germination
and robustness of the seedling.
Interaction of Nano-TiO 2 with Plants: Preparation and Translocation
79