nano-agriculture – carbon nanotubes enhance tomato seed

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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.



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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