01 March 2011
Carbon nanotubes can enhance plant growth without damaging plant cells, say scientists from India.
Sabyasachi Sarkar and colleagues from the Indian Institute of Technology in Kanpur treated chickpea plants with up to 6ug/ml of water soluble carbon nanotubes. They found that the nanotubes increased the growth rate in every part of the plant - in the roots, shoots and branches.
Root length, shoot length, number of roots and water uptake by plants were monitored for 10 days. Left: no nanotubes, middle: 200ul nanotubes, right: 100ul nanotubes
Fluid and nutrient uptake by young plants is increased under the influence of the nanotubes, explains Sarkar. The nanotubes make channels present in the plants more prominent to enhance the flow of water and other soluble materials. 'It's like feeding the young with a spoon,' adds Sarkar, who was inspired by trees growing near his home. 'I wanted to see the channels responsible for lifting water in the tall eucalyptus trees outside my house,' he says.
Sarkar thought that the channels could be replicated by carbon nanotubes. 'We followed Thomas Edison's recipe to make carbonised filament from bamboo or wood wool in his electric bulb to get the carbon nanotubes,' he adds. 'Of course, we had to derivatise them to make them water soluble.' The team achieved this by attaching carboxylic acid groups to the surface of the tubes.
The nanotubes could be used to study plant disease and growth problems by adding fluorescent materials to them before they are introduced to the plants. The channels could then produce fluorescent images. The technique could aid water conservation, adds Sarkar, by measuring the optimum water needed to grow healthy plants.
One problem that the team faces is the possible toxicity of the carbon nanotubes. 'Reports of cell damage caused by non-degradable carbon nanotubes have led to a myth about nanotubes being toxic,' says Sarkar. He goes on to explain that while ultra pure (surface defect free) carbon nanotubes are strong and can puncture cells and stay inside permanently causing problems, the water soluble versions are non-toxic to cells.
'The work seems to support the positive effect of carbon nanotubes,' says Xiaohong Fang, an expert in the use of carbon nanotubes as molecular transporters in plants at the Chinese Academy of Sciences in China. However, she points out that the biological effects on plants may differ depending on the materials' chemical and physical properties, plant type and cultivation conditions. 'More mechanistic studies are needed to discover whether carbon nanomaterials are helpful or harmful to plants,' she adds.
Sarkar hopes that the water soluble carbon nanotubes will be used to map and treat plant disease; to improve hydroponic crops (cultivation of plants in nutrient solution rather than in soil); drought and salinity tolerance; and phytoremediation (using plants to decontaminate soil and water from toxic chemicals).