Engineers at the Massachusetts Institute of Technology have made another extraordinary breakthrough. They have developed sensors that can be printed on the leaf of a plant. The sensors signal when a water shortage occurs. This technology can not only save neglected houseplants but, more importantly, give growers timely warning if their crops are at risk due to water shortage.
When soil dries out, the growth process of plants slows down, photosynthetic activity decreases and damages the plants' tissues. Some plants then start to wilt but there are also plants that show almost nothing. It is often too late by then.
Plant stomata
MIT's new sensors use the plant's stomata (stomata): these are tiny pores in the surface of a leaf that allow water to evaporate. As water evaporates from the leaf, water pressure in the plant drops, allowing water to be drawn from the soil: a process called transpiration. Plant biologists know that stomata open when exposed to light and close in the dark, but the dynamics of this mechanism have not yet been much studied.
'We already know that stomata respond to light, to CO2 concentration and to drought but now we have been able to monitor it continuously,' says lead author Volodymyr Koman. 'Previous methods were not able to give this kind of information.'
Ink and electricity
To create the sensor, the scientists used an ink made of carbon nanotubes; tiny hollow tubes of carbon that conduct electricity - dissolved in an organic compound called sodium dodecyl sulphate, which does not damage stomata. Ink can be printed over the pore, creating an electronic circuit. If the pore closes, the circuit is intact and the current can be measured with a multimeter. If the pore zcih opens, the circuit is broken and the current stops. This allows researchers to measure very precisely when a pore opens and closes. By measuring this opening and closing for a few days - under normal and dry conditions - in succession, the researchers found that they can detect within two days whether a plant lacks water. They found that it takes stomata about seven minutes to open after exposure to light and 53 minutes to close after dark, but these responses change in dry conditions. When plants are water-deficient, it takes the stomata 25 minutes to open, while the time to close drops to 45 minutes.
The researchers tested the sensors on the so-called spoon plant, mainly because it has large stomata. To apply the ink to the leaves, the team had developed a printing mould with a microfluidic channel. When the mould is placed on a leaf, the ink flowing through the channel is applied to the leaf surface. The scientists are now working on a new way to apply the electronic circuits, which is by simply placing a sticker on the leaf surface. That way in particular could be useful for growers and agricultural producers, also with it to future climate changes (including more droughts).
Quick indication
'It looks like this is the earliest indicator of drought that exists for agriculutral applications,' said Michael Strano, one of the scientists involved. 'It's hard to get this information any other way. You can put sensors in the ground and use satellites and mapping, but with that you will never know exactly what a specific plant detects as its water potential.'
It is already working with a major agricultural manufacturer to make these sensors for growers. Strano thinks the technology could also be useful for gardeners and urban farmers. In addition, it could help researchers discover new ways to develop drought-resistant plants.
By: Kelly Bakker
Source + photo: MIT
