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RESEARCH NEWS
CURRENT SCIENCE, VOL. 99, NO. 3, 10 AUGUST 2010 274
Nano-agriculture – carbon nanotubes enhance tomato seedgermination and plant growth
C. Srinivasan and R. Saraswathi
Agriculture is an area where new tech-
nologies are often applied to improve the
yield of crops. Genetically modified
(GM) crops have received mixed reac-
tions from the public, particularly the
farmers. The recent approval of Bt -
brinjal seeds by the government triggered
a lot of dissent among farmers and the
public quickly prompting the government
to withdraw its decision. (For a detailed
discussion on Bt -brinjal, see ref. 1.)
Nano-agriculture involves the employ-
ment of nanoparticles in agriculture with
the ambition that these particles will im-
part some beneficial effects to the crops.
Carbon nanotubes (CNTs) have acquired
an important status in nanotechnology
due to their unique mechanical, elec-
tronic and thermal properties, which
have led to their exploitation in diverse
applications such as sensors, flat panel
displays, energy and gas storage2. Also,
their application in drug delivery and
medical diagnostics is being actively
explored. The study on the effects of
nanoparticles in plant science is a newlyemerging area of research3–5. Recently,
confocal fluorescence image studies
have revealed the capacity of single-
walled carbon nanotubes (SWNTs) to
traverse across both the plant cell wall
and cell membrane6. This study also
pointed out that SWNTs can serve as
effective nanotransporters to deliver
DNA and small dye molecules into intact
plant cells. There are also some reports
on other nanoparticles as smart treat-
ment-delivery systems in plants7. Com-
pared to plant cell walls and membranes,
the penetration of nanoparticles into
seeds is expected to be difficult due to
the significantly thick seed coat covering
the whole seed. In spite of this anti-
cipated hurdle, Khodakovskaya et al.8
demonstrated that CNTs could effec-
tively penetrate seed coat, thereby influ-
encing the seed germination and plant
growth. This study commendably esta-
blished that exposure of seeds to CNTs
resulted in the enhanced tomato seed
germination and growth rate. The experi-
ment involved placing sterile tomato
seeds on standard agar Murashige andSkoog medium (MS medium) with
different concentrations (10, 20 and
40 μg/ml) of added multi-walled carbon
nanotubes (MWNTs) and also without
nanotubes. It is amazing to note that the
seeds placed in the MS medium with the
given three concentrations of CNTs
sprouted on the third day whereas the
seeds in the control experiment (without
CNTs) did not germinate in the same
period (Figure 1 a). Also, in the next few
days the germination rate in CNTs sup-
plemented medium was significantly
higher than that observed for the control
sample (Figure 1 b). The germination
percentage for seeds that were placed on
regular medium averaged 71 in 20
days, whereas germination percentage of
the seeds placed on medium supple-
mented with CNTs (40 μg/ml) averaged
90 during the same period.
Tomato plants grown in media sup-
plemented with CNTs not only showed
an increase in biomass but also possessed
well-developed long stems compared to
the control (Figure 2 b). However, the
length of the roots was found to be the
same in both cases (Figure 2 a) indicat-
ing the absence of any toxic effects of
CNTs on root development and root
elongation in the concentration range
studied. Khodakovskaya et al.8 thus
demonstrated that CNTs exposed seeds
germinated up to two times faster than
control seeds and the seedlings weighed
more than twice as much as the untreated
plants. These desirable effects possibly
Figure 1. Effect of CNTs on tomato seed germination. a , Tomato seeds incubated dur-ing 3 days without (left) or with (right) CNTs on MS medium. b , Time of germination andgermination percentages of seeds incubated with and without CNTs during 20 days. Re-
printed with permission from Khodakovskaya et al.8. Copyright (2010) from AmericanChemical Society.
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RESEARCH NEWS
CURRENT SCIENCE, VOL. 99, NO. 3, 10 AUGUST 2010 275
occurred due to the penetration of the
nanotubes into the seed coat enhancing
water uptake by the seed. Raman spectralstudy was used to confirm that CNTs
penetrate tomato seeds. Tomato seeds
incubated in agar media supplemented
with CNTs for two days were washed,
dried and cut, and the surface was exam-
ined by Raman spectroscopy. The obser-
vation of the G band at 1569 cm–1 in the
Raman spectrum confirmed the presence
of CNTs inside the seed. No such band
was seen for the control sample. Trans-mission electron microscopy imaging
also confirmed the presence of CNTs
inside the seed. Thermogravimetric
analysis revealed that the seeds incu-
bated in CNTs for two days possessed a
moisture content of 57.6% compared to
the value of 38.9% for the control. One
reason suggested for the higher water
uptake was that new pores were gener-
ated during penetration of seed coat by
CNTs, which aided better water permea-
tion. Another possible cause could be the
efficient gating of the water channelsby the CNTs in the seed coat. Such a
hypothesis however requires further sub-
stantiation by suitable experimental data.
An immediate outcome of the study is
the observation of increased biomass,
which will have some important eco-
nomic significance in the production of
biofuels. Also the rapid germination and
growth rates will yield agriculture pro-
ducts in a short duration.
It has to be emphasized that the tech-
nology described here cannot be imme-
diately implemented in agriculture.
Several issues need to be addressed. It is
necessary to know how the plants deve-
loped by this technique will fight pests.
It has to be investigated whether CNT
treated plants can harm other plants in
the same field. Finally, it must be defi-
nitely established that CNTs are not toxic
to plants and the tomatoes obtained by
this technology will not harm mankind.
1. Yadugiri, V. T., Curr. Sci., 2010, 98, 1273.
2. Ohashi, T. and Dai, L., Carbon Nanotech-
nology (ed. Dai, L.), Elsevier, The Nether-
lands, 2006.
3. Zheng, L., Hong, F., Lu, S. and Liu, C.,
Biol. Trace Elem. Res., 2005, 104, 83.
4. Lin, D. and Xing, B., Environ. Pollut.,
2007, 150, 243.
5. Yang, L. and Watts, D. J., Toxicol. Lett.,
2005, 158, 122.
6. Liu, Q., Chen, B., Wang, Q., Shi, X., Xiao,
Z., Lin, J. and Fang, X., Nano Lett ., 2009,
9, 1007.
7. Gonzales-Melendi, P. et al., Ann. Bot .,
2008, 101, 187.
8. Khodakovskaya, M., Dervishi, E.,
Mahmood, M., Xu, Y., Li, Z., Watanabe,
F. and Biris, A. S., ACS Nano, 2009, 3,
3221.
C. Srinivasan* and R. Saraswathi are in
the Department of Materials Science,
Madurai Kamaraj University, Madurai
625 021, India.
*e-mail: [email protected]
Figure 2. a , 27-day-old tomato seedlings growing on medium with and without CNTs. b ,25-day-old tomato seedlings growing on medium without and with CNTs. Concentrationof CNTs in growth medium in μg/ml is shown below each figure. Reprinted with permis-sion from Khodakovskaya et al.
8. Copyright (2010) f rom American Chemical Society.
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