EFFECTS OF NANOFERTILIZERS ON PLANT GROWTH AND DEVELOPMENT, AND THEIR INTERRELATIONSHIP WITH THE ENVIRONMENT - Fertilizers: Components, Uses in Agriculture and Environmental Impacts - page 218

showing a mitotic index reduction and concentration-dependent increase in the aberration
emergence, which evidenced a nano-TiO 2 -induced genotoxic effect for both species.
Carbon nanotubes have shown promise as regulators of seed germination and plant
growth (Khodakovskaya et al., 2012). Begum et al. (2012) evaluated the possible
phytotoxicity of multi-walled carbon nanotubes (MWNTs) at 0, 20, 200, 1,000, and 2,000 mg
L -1 with red spinach, lettuce, rice, cucumber, chili, lady's finger, and soybean based on root
and shoot growth, cell death, and electrolyte leakage at the seedling stage. They reported that
red spinach and lettuce were most sensitive to MWNTs, followed by rice and cucumber,
while very few or no toxic effects were observed for chili, lady's finger, and soybean.
We found that, compared with the control, magnetite and hematite significantly increased
the seed germination rate of oregano when the seeds were irrigated at 1.6 and 1.0 g L -1 ,
respectively (Figure 1). In addition, solutions of 1.6 and 3.0 g magnetite L -1 as well as 1.0,
1.6, and 3.0 g hematite L -1 substantially increased the seed germination rates of parsley and
snapdragon, compared with the control (Figure 1). We found that hematite's effects were
equal to or greater than magnetite's effects on seed germination rate. We also found that plant
species differ in their susceptibility to different kinds of nanoparticles, as witnessed by the
seed germination rate. Low concentrations of magnetite, i.e., 0.3, 0.5, and 1.0 g L -1 , did not
stimulate certain physiological changes during the seed germination as observed by the
germination rates of parsley and snapdragon. This observation notwithstanding, our results
indicated that an appropriate concentration of nanoparticles could promote the seed
germination of some plants. Additionally, Kumar et al. (2013) found a considerable
correlation between the expression of key plant regulatory molecules, microRNAs, seed
germination, growth, and the antioxidant potential of A. thaliana on exposure to gold
nanoparticles. These results suggest that the increasing release of nanoparticles into the
environment could have positive effects on the seed germination rates in some cultivated
plants. Furthermore, there was no evidence of nanotoxicity in plants when low or high
nanoparticle doses were evaluated.
We determined that, compared to the control treatment, the nanoparticles of magnetite,
hematite, ferrihydrite, zinc oxide, and titanium dioxide had a significant effect on a number of
plant characteristics during the early stages of common bean, maize, and sunflower under
greenhouse conditions ( P < 0.05; Table 2). Seedling emergence, fresh weight of the shoot,
and chlorophyll content decreased significantly ( P < 0.05) in maize, common bean, and
sunflower plants when the soil was irrigated with hematite nanoparticles (Table 2). However,
the effect was insignificant when other nanoparticles were used during the irrigation process.
Titanium dioxide, a well-known photocatalyst, has been widely studied for its possible
enhancement of photosynthesis (Narayanan et al., 2013). Su et al. (2007) showed that suitable
concentrations of nano-anatase TiO 2 can improve the oxygen evolution in spinach plants.
This phenomenon may be attributed to the increase in light absorbance and energy transfer
among the amino acids. Similar results were demonstrated with nano-TiO 2 on wheat plants
(Moaveni et al., 2011). However, our results showed that the chlorophyll content was
significantly equal to the control treatment when plants were irrigated with TiO 2 (Table 2).
Jacob et al. (2013) revealed that the exposure of common bean and wheat to TiO 2
nanoparticles did not affect biomass production, but did substantially increase root Ti sorption
and uptake.