268
catalase, and glutathione peroxidase (Hong et al. 2005b; Lei et al. 2008). Hence,
TiO 2 NPs could maintain plant growth in prevailing stress conditions.
Likewise, CNTs were reported to alleviate the Cd stress by regulating the accumulation of various cations and organic solutes. CNT counterbalanced the cadmium
stress by enhancing the K
+
and Ca
+
concentrations and reducing the levels of proline
and soluble carbohydrates (Chai et al. 2013). Similarly, MWCNTs and C 60 fullrenes
reduced the pesticide absorption of zuchhini, corn, tomato, and soybean plants.
These nanostructures have high affinity for hydrophobic pesticides, chlordane and
DDx, and thus prevent their uptake by plants (Torre-Roche et al. 2013). The nanocomposite Ag@dsDNA@GO was found to impart bacterial resistance to tomato
plants. GO nonspecifically interacted with the bacteria and wrapped it by inducing
deformation in its rod-shaped structure. While Ag induced cell membrane destruction and provided bacterial tolerance to plants. Nanocomposites were found to
reduce the viability of X. perforans in culture as well as on plants. Thus, nanocomposites maintained the tomato growth and yield in X. perforans-infected tomato
(Ocsoy et al. 2013).
10.3.2 Mechanism Underlying the Negative Effects of NPs
on Plants
Various reports have documented the growth-inhibitory effect of NPs on plants
(Table 10.2). The mechanism underlying the phytotoxic nature of NPs is discussed
as under.
NPs Reduced Chlorophyll Content and Inhibited Photosynthesis
Ferrophase magnetic NPs were inhibiting the growth of maize plants by influencing
their photosynthetic reactions. NPs penetrated the nuclear biomembrane and interfered with the nucleic acid biosynthesis. The magnetic properties of NPs also influenced the transmembrane ion flow and affected the structure of enzymes involved in
photosynthesis. NPs also altered the metabolism at various tissue levels (Racuciu
and Creanga 2007, 2009b). Likewise, the exposure of Ag NPs altered the biochemical composition of B. monneri to induce stress. Exposure of Ag NPs decreased the
total phenolic, protein, and carbohydrate content of plants. NPs also reduced the
level of proteins associated with the photosystem, starch synthesis system, and carbohydrate translocation machinery (Krishnaraj et al. 2012). The response of NPs on
plants can further vary depending upon the environmental and exposure conditions.
The growth inhibitory effects of TiO 2 , CeO 2 , and Cu(OH) 2 NPs to Clarkia unguiculata were noticed at some specific conditions. Exposure of TiO 2 and CeO 2 at maximum plant growth period, high light, and nutrient conditions disrupted the energy
transfer from photosystem II (PSII) to the Calvin cycle. As a result, the
V. Kumar et al.
catalase, and glutathione peroxidase (Hong et al. 2005b; Lei et al. 2008). Hence,
TiO 2 NPs could maintain plant growth in prevailing stress conditions.
Likewise, CNTs were reported to alleviate the Cd stress by regulating the accumulation of various cations and organic solutes. CNT counterbalanced the cadmium
stress by enhancing the K
+
and Ca
+
concentrations and reducing the levels of proline
and soluble carbohydrates (Chai et al. 2013). Similarly, MWCNTs and C 60 fullrenes
reduced the pesticide absorption of zuchhini, corn, tomato, and soybean plants.
These nanostructures have high affinity for hydrophobic pesticides, chlordane and
DDx, and thus prevent their uptake by plants (Torre-Roche et al. 2013). The nanocomposite Ag@dsDNA@GO was found to impart bacterial resistance to tomato
plants. GO nonspecifically interacted with the bacteria and wrapped it by inducing
deformation in its rod-shaped structure. While Ag induced cell membrane destruction and provided bacterial tolerance to plants. Nanocomposites were found to
reduce the viability of X. perforans in culture as well as on plants. Thus, nanocomposites maintained the tomato growth and yield in X. perforans-infected tomato
(Ocsoy et al. 2013).
10.3.2 Mechanism Underlying the Negative Effects of NPs
on Plants
Various reports have documented the growth-inhibitory effect of NPs on plants
(Table 10.2). The mechanism underlying the phytotoxic nature of NPs is discussed
as under.
NPs Reduced Chlorophyll Content and Inhibited Photosynthesis
Ferrophase magnetic NPs were inhibiting the growth of maize plants by influencing
their photosynthetic reactions. NPs penetrated the nuclear biomembrane and interfered with the nucleic acid biosynthesis. The magnetic properties of NPs also influenced the transmembrane ion flow and affected the structure of enzymes involved in
photosynthesis. NPs also altered the metabolism at various tissue levels (Racuciu
and Creanga 2007, 2009b). Likewise, the exposure of Ag NPs altered the biochemical composition of B. monneri to induce stress. Exposure of Ag NPs decreased the
total phenolic, protein, and carbohydrate content of plants. NPs also reduced the
level of proteins associated with the photosystem, starch synthesis system, and carbohydrate translocation machinery (Krishnaraj et al. 2012). The response of NPs on
plants can further vary depending upon the environmental and exposure conditions.
The growth inhibitory effects of TiO 2 , CeO 2 , and Cu(OH) 2 NPs to Clarkia unguiculata were noticed at some specific conditions. Exposure of TiO 2 and CeO 2 at maximum plant growth period, high light, and nutrient conditions disrupted the energy
transfer from photosystem II (PSII) to the Calvin cycle. As a result, the
V. Kumar et al.