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decreased. These factors collectively resulted in overall increase in the rate of photosynthesis on TiO 2 NP exposure under heat stress (Qi et al. 2013).
NPs Change Genetic Material Expression
TiO 2 NPs increased the messenger RNA (mRNA) expression of both small (rbcS)
and large (rbcL) subunits of RUBISCO in spinach. The protein expression and
enzyme activity of RUBISCO was 2.33 times higher in TiO 2 NP-treated plants than
control plants (Xuming et al. 2008). While Au NPs were found to enhance the seed
yield and vegetative growth of A. thaliana by inducing the key plant-regulating
molecules, microRNAs. Exposure of Au NPs induced alteration in the expression of
microRNAs related to plant growth and development (Kumar et al. 2013). SWCNHs
regulated the expression of stress responses, cellular responses, and metabolic processes to enhance the seed germination and growth of various crop plants (Lahiani
et al. 2015). The tobacco cell growth-enhancing effect of MWCNTs was due to the
upregulation of CycB, NtLRX1, and aquaporin genes. Unregulated genes increased
the water transport and cell division of treated cells as compared to control tobacco
cells (Khodakovskaya et al. 2012).
NPs Mediated Increase in Nutrient Absorption
Citric acid-coated CeO 2 NPs have enhanced the growth parameters of radish seedlings by increasing the macro- and micronutrient absorption of plants. Coated NPs
also increased the water uptake of roots and resulted in their increased biomass.
Noncoated CeO 2 NPs, however, aggregated in the medium and induced toxicity
(Trujillo-Reyes et al. 2013). Tire rubber ash NPs release zinc and iron that increased
their availability to cucumber. As zinc and iron are important for growth and development of plants, NP exposure was indirectly enhancing the root–shoot growth of
cucumber plants (Moghaddasi et al. 2015).
NPs Changed Cell Architect
CeO 2 NPs were observed in the form of cerium perhydroxide in the cell wall and
intercellular spaces of epidermal and cortical cells of C. sativum plants. However,
their presence was not indicated in the meristematic tissues. Hence, decreased enzymatic stress in the growing zone was responsible for the enhanced growth of plants
on CeO 2 exposure (Morales et al. 2013). Exposure of MWCNTs induced cellular
elongation of root cells and increased the activity of dehydrogenase enzyme of
wheat plants (Wang et al. 2012a). Exposure of Fe NPs was reported to induce root
elongation by free radical-mediated cell wall loosening of A. thaliana roots. NPs
induced cell wall loosening by generation of H 2 O 2 that released OH free radicals
and degraded the pectin-polysaccharides of plant roots. NPs also induced more
V. Kumar et al.
decreased. These factors collectively resulted in overall increase in the rate of photosynthesis on TiO 2 NP exposure under heat stress (Qi et al. 2013).
NPs Change Genetic Material Expression
TiO 2 NPs increased the messenger RNA (mRNA) expression of both small (rbcS)
and large (rbcL) subunits of RUBISCO in spinach. The protein expression and
enzyme activity of RUBISCO was 2.33 times higher in TiO 2 NP-treated plants than
control plants (Xuming et al. 2008). While Au NPs were found to enhance the seed
yield and vegetative growth of A. thaliana by inducing the key plant-regulating
molecules, microRNAs. Exposure of Au NPs induced alteration in the expression of
microRNAs related to plant growth and development (Kumar et al. 2013). SWCNHs
regulated the expression of stress responses, cellular responses, and metabolic processes to enhance the seed germination and growth of various crop plants (Lahiani
et al. 2015). The tobacco cell growth-enhancing effect of MWCNTs was due to the
upregulation of CycB, NtLRX1, and aquaporin genes. Unregulated genes increased
the water transport and cell division of treated cells as compared to control tobacco
cells (Khodakovskaya et al. 2012).
NPs Mediated Increase in Nutrient Absorption
Citric acid-coated CeO 2 NPs have enhanced the growth parameters of radish seedlings by increasing the macro- and micronutrient absorption of plants. Coated NPs
also increased the water uptake of roots and resulted in their increased biomass.
Noncoated CeO 2 NPs, however, aggregated in the medium and induced toxicity
(Trujillo-Reyes et al. 2013). Tire rubber ash NPs release zinc and iron that increased
their availability to cucumber. As zinc and iron are important for growth and development of plants, NP exposure was indirectly enhancing the root–shoot growth of
cucumber plants (Moghaddasi et al. 2015).
NPs Changed Cell Architect
CeO 2 NPs were observed in the form of cerium perhydroxide in the cell wall and
intercellular spaces of epidermal and cortical cells of C. sativum plants. However,
their presence was not indicated in the meristematic tissues. Hence, decreased enzymatic stress in the growing zone was responsible for the enhanced growth of plants
on CeO 2 exposure (Morales et al. 2013). Exposure of MWCNTs induced cellular
elongation of root cells and increased the activity of dehydrogenase enzyme of
wheat plants (Wang et al. 2012a). Exposure of Fe NPs was reported to induce root
elongation by free radical-mediated cell wall loosening of A. thaliana roots. NPs
induced cell wall loosening by generation of H 2 O 2 that released OH free radicals
and degraded the pectin-polysaccharides of plant roots. NPs also induced more
V. Kumar et al.