Plant ECG – when plants sound the alarm
Although plants do not have a nervous system, they are nevertheless able to transmit and process electrical signals in the organism. The signals are generated in relation to catching prey and fending off enemies as well as in the production and release of fragrances that the plants use to communicate with each other. Lehner GmbH, based in Kirchheim, develops sensor systems for use in plant cultivation that are able to detect specific electrical signals.
The plant ECG can be used to detect mildew infestation on grapevines. (© Lehner GmbH)
Lehner Jr. is a biotechnology specialist who did his doctoral thesis on circadian rhythms in plants (roughly 24-h cycle). The thesis was partially financed by the DFG and Lehner's supervisor was Prof. Dr. Edgar Wagner, a leading light in chronobiology. Wagner examined the day- and night rhythms in Chenopodium (goosefoot). At night, the plant's leaves are closed (night position) and during the day they open up (day position). "We found that longitudinal growth happens at defined periods of time. Different daylight periods affect the formation of flowers and the plants' longitudinal growth. It is also known that the onset of flower formation is influenced by the duration of daylight as sensed by the leaves. The phenomena of growth, leaf position and onset of flower formation are closely linked," explained Lehner.
These findings led to new questions: if the leaf position and the longitudinal growth of the stem function are indicators of the onset of flowering, how are these two processes linked? “We wanted to know whether electrical signals played a part in this phenomenon. Although electrical signals in plants have been known for quite some time, they have not been specifically analysed,” said Lehner going on to add that this approach required the development of a system that enabled long-term measurements without damaging or affecting the plant in any way. “Any damage to the plant triggers signals that can falsify the measurement results. That is why we had to find a very gentle method,” said Lehner.
And so the plant ECG was born. Just like human ECG systems, the plant ECG has electrodes that are attached to the plants. Different versions of electrodes have been developed in order to avoid using invasive methods. “For goosefeet, we use the same contact gels that doctors use for ECGs. However, these contact gels do not work with Arabidopsis and a number of other plants,” said Lehner explaining that the contact agents used need to be adapted to the requirements of individual plant species. However, as he pointed out, the registration of signals and the principle of signal analysis are the most difficult processes. “We have to prepare a specific electrophysiogramme for each individual plant species, containing the characteristic signalling patterns of the different plant states. The fact that electrical signals in plants follow their own regularities needs to be taken into consideration. In goosefeet, it takes up to five minutes before an action potential is generated.”
The perfect early warning system
This sensor system is used to register electrical signals on a grapevine. (© Lehner GmbH)
Lehner finally managed to register action and variation potentials and characterise their distribution throughout the day. He was also able to show that certain signalling patterns correlated with the onset of flowering induction in goosefeet. "This means that electrophysiogrammes can be used to assess the onset of flowering and fruit formation, long before the flowers are visible." The researchers are now aware of a broad range of specific signalling patterns that occur as a result of certain environmental stimuli such as water shortage: "Extreme water stress leads to a high-frequency series of action potentials," said Lehner.
Signalling patterns related to the infestation of the plants by pests are of great interest for commercial plant cultivation. The infestation of grapevines with mildew leads to characteristic action potential patterns. It may be just a distant dream, but perhaps one day vineyards will be equipped with sensor systems that sound an alarm when the dreaded fungus appears. The great advantage of systems like these is that the winegrowers would be able to treat the affected plants, thus preventing the fungus from spreading to other plants. The ideal-case scenario would be the attachment of the sensor system to a radio network, which would send a text message to the winegrower as soon as a pest makes its first devastating move. Lehner GmbH is currently developing measurement systems for such applications that it hopes to launch in 2010. Lehner estimates that the systems will cost a few hundred euros, "when used for a homogeneous area the size of a football field where ten plants are equipped with a measurement unit." The plants that are thus equipped would serve as indicators for the state of all plants on a particular area.
Controlling the onset of flowering –without the help of genetic engineering
Lehner is already thinking far beyond these alarm systems, in the belief that the ability to measure electrical signals also means that the signals can be manipulated. “We are already able to trigger the onset of flowering using specific electrical stimulations. In order to do this, plants have to be at a particular stage in their development. We assume that in addition to stimulating the onset of flowering, we will also be able to delay the formation of flowers by applying certain disturbing signals,” said Lehner. One interesting application for Lehner’s system might be to delay the onset of flowering until weather conditions are more favourable, for example when there is no frost.
Lehner’s vision: electrophysiogramme databases for all plant species to help users trigger or delay the onset of flowering and collect information about the physiological state and requirements of their plants.
Help for self-help
Another project Lehner and one of his new partners are hoping to focus on is the defence against herbivores, for example in crops such as corn. Over the last few years, the Western corn rootworm from the Balkans has become a serious problem for German corn growers. These insects feed on the corn plants and destroy entire harvests. “Western corn rootworm infestations are expected to result in a very special signalling pattern, because when rootworms feed, considerable tissue damage occurs,” said Lehner who is not only considering the development of an alarm sensor. He also believes that the best prophylaxis would be to electrically trigger healthy plants to produce a signalling substance that attracts the rootworm’s enemies. We are aiming to find a way to imitate the electrical triggers and transmit them to healthy plants,” said Lehner explaining that this helps the plants to defend themselves – in the ideal-case scenario this would be entirely without the use of chemicals.
A contribution from:
LEHNER GmbH Sensor Systeme
Dr. Lars Lehner
Tel.: +49 (0)7021 97013-21