260
was drastically decreased for the next three generations. However, no morphological alteration in the NP-exposed plants was evident (Geisler-Lee et al. 2014).
MWCNTs have induced reduction in shoot and root length of red spinach, lettuce, rice, and cucumber plants. Further, cell death and electrolyte leakage were also
noticed in these plants (Begum et al. 2012). MWCNTs were also reported to reduce
seed germination, seedling growth, and development of barley, corn, and soybean
(Lahiani et al. 2013). CeO 2 and TiO 2 did not affect the seed germination but reduced
root elongation in Hordeum vulgare L (Mattiello et al. 2015). Ag NPs have inhibited
the overall vegetative growth of Crambe abyssinica (Ma et al. 2015). CuO NPs also
inhibited the growth of the maize plant. The NPs, however, have no effect on seed
germination (Wang et al. 2012b). Citrate-capped Ag NPs inhibited maize seed germination. ZnO NPs did not affect the germination of maize. Both ZnO and Ag NPs
induced deformation of root cells and irregular growth of maize roots (Pokhrel and
Dubey 2013). Ag NPs inhibited the Triticum aestivum L. seedling growth. NPs also
altered the morphology of root tip cells (Vannini et al. 2014).
Negative Effect of NPs on Plant Biomass and Chlorophyll Content
There are several reports documenting the influence of NP exposure on biomass,
vegetative growth, and physiological aspects, such as chlorophyll accumulations of
plants. Exposure of MWCNTs and C 70 fullerenes in combination with natural
organic matter was reported to retard plant growth and extend the flowering time
and maturity age of rice seeds (Lin et al. 2009a). ZnO NPs has induced reduction in
Lolium perenne (ryegrass) biomass. Further, the NPs induced shrinkage of root tips
and collapse of root epidermal and cortical cells (Lin and Xing 2008). ZnO NPs
induced reduction in biomass weight and induced damage to Fagopyrum esculentum roots (Lee et al. 2013). Cucurbita pepo (zucchini) plants exposed to hydroponic
suspension of Ag NPs have also shown growth retardation. Exposure of Cu NPs has
induced reduction in root length and plant biomass accumulation. While Ag NP
exposure decreased the transpiration rate in addition to reduction in plant biomass
(Stampoulis et al. 2009). Exposure of variously sized MWCNT agglomerates
showed size-dependent deteriorating effect on dry weight, viability, and chlorophyll
content of T87 A. thaliana suspension cells. MWCNTs also lowered the activity of
superoxide dismutase enzyme of these cell lines in a size-dependent manner (Lin
et al. 2009b). Perchloric acid-coated iron oxide NPs have reduced the chlorophyll a/
chlorophyll b ratio of maize plants. NP exposure also reduced the stem length.
These variations along with stimulation of nucleic acid biosynthesis were more pronounced in the presence of electromagnetic field (Racuciu et al. 2009). Exposure of
C 60 fullerenes was found to reduce the growth, chlorophyll content, and chloroplast
oxygen production of aquatic plant, Lemna gibba (Santos et al. 2013). C 60 fullerenes
are thus documented as a threat to the aquatic ecosystem.
TiO 2 NPs were found to reduce the fresh and dry weight contents of wheat shoots
and roots. Further, reduction in the chlorophyll content of exposed plants was
noticed (Mahmoodzadeh et al. 2013). Tomato plants exposed to Ag, Co, Ni, CeO 2 ,
Fe 3 O 4 , SnO 2 , and TiO 2 NPs also showed reduction in stem length. Additionally,
V. Kumar et al.
was drastically decreased for the next three generations. However, no morphological alteration in the NP-exposed plants was evident (Geisler-Lee et al. 2014).
MWCNTs have induced reduction in shoot and root length of red spinach, lettuce, rice, and cucumber plants. Further, cell death and electrolyte leakage were also
noticed in these plants (Begum et al. 2012). MWCNTs were also reported to reduce
seed germination, seedling growth, and development of barley, corn, and soybean
(Lahiani et al. 2013). CeO 2 and TiO 2 did not affect the seed germination but reduced
root elongation in Hordeum vulgare L (Mattiello et al. 2015). Ag NPs have inhibited
the overall vegetative growth of Crambe abyssinica (Ma et al. 2015). CuO NPs also
inhibited the growth of the maize plant. The NPs, however, have no effect on seed
germination (Wang et al. 2012b). Citrate-capped Ag NPs inhibited maize seed germination. ZnO NPs did not affect the germination of maize. Both ZnO and Ag NPs
induced deformation of root cells and irregular growth of maize roots (Pokhrel and
Dubey 2013). Ag NPs inhibited the Triticum aestivum L. seedling growth. NPs also
altered the morphology of root tip cells (Vannini et al. 2014).
Negative Effect of NPs on Plant Biomass and Chlorophyll Content
There are several reports documenting the influence of NP exposure on biomass,
vegetative growth, and physiological aspects, such as chlorophyll accumulations of
plants. Exposure of MWCNTs and C 70 fullerenes in combination with natural
organic matter was reported to retard plant growth and extend the flowering time
and maturity age of rice seeds (Lin et al. 2009a). ZnO NPs has induced reduction in
Lolium perenne (ryegrass) biomass. Further, the NPs induced shrinkage of root tips
and collapse of root epidermal and cortical cells (Lin and Xing 2008). ZnO NPs
induced reduction in biomass weight and induced damage to Fagopyrum esculentum roots (Lee et al. 2013). Cucurbita pepo (zucchini) plants exposed to hydroponic
suspension of Ag NPs have also shown growth retardation. Exposure of Cu NPs has
induced reduction in root length and plant biomass accumulation. While Ag NP
exposure decreased the transpiration rate in addition to reduction in plant biomass
(Stampoulis et al. 2009). Exposure of variously sized MWCNT agglomerates
showed size-dependent deteriorating effect on dry weight, viability, and chlorophyll
content of T87 A. thaliana suspension cells. MWCNTs also lowered the activity of
superoxide dismutase enzyme of these cell lines in a size-dependent manner (Lin
et al. 2009b). Perchloric acid-coated iron oxide NPs have reduced the chlorophyll a/
chlorophyll b ratio of maize plants. NP exposure also reduced the stem length.
These variations along with stimulation of nucleic acid biosynthesis were more pronounced in the presence of electromagnetic field (Racuciu et al. 2009). Exposure of
C 60 fullerenes was found to reduce the growth, chlorophyll content, and chloroplast
oxygen production of aquatic plant, Lemna gibba (Santos et al. 2013). C 60 fullerenes
are thus documented as a threat to the aquatic ecosystem.
TiO 2 NPs were found to reduce the fresh and dry weight contents of wheat shoots
and roots. Further, reduction in the chlorophyll content of exposed plants was
noticed (Mahmoodzadeh et al. 2013). Tomato plants exposed to Ag, Co, Ni, CeO 2 ,
Fe 3 O 4 , SnO 2 , and TiO 2 NPs also showed reduction in stem length. Additionally,
V. Kumar et al.