Unlike humans and animals, plants do not have a nervous system. Nevertheless, they also react to touch and other stress factors with electrical signals. In some plants, these signals even trigger rapid movements. For example, the carnivorous Venus flytrap (Dionaea muscipula) can snap its trapping leaf shut within 100 milliseconds, performing one of the fastest known movements in the plant world.
Researchers from Linköping University and Columbia University have now developed technology that allows them to measure the generation and propagation of electrical signals in a Venus flytrap. The new device consists of a film containing electrodes that is so thin that it can be adjusted to the curvature of the trapping leaf when attached to the plant. How this so-called multi-electrode array is attached can be seen in the picture.
Small feelers sit on the inside of the catching leaf of a Venus flytrap. The trap only closes if these are touched at least twice within a period of about 30 seconds. With a simple stimulus, which can easily be triggered by something other than a potential prey, the plant will not collapse, thus conserving energy. Insects that fall into the trap, on the other hand, are trapped and decomposed by digestive enzymes.
Bending a tentacle causes an electrical signal that causes ions, electrically charged atoms or molecules, to rush through the plant’s cell membranes. The rapid change in electrical voltage between the cell interior and the cell environment leads to an impulse that spreads through the plant. In their experiments, the scientists touched a sensory hair and used around 30 electrodes to measure the signal that was triggered. At the same time, they filmed the movement of the trap in order to investigate the connection between the closing of the trap leaf and the electrical signal.
In previous research in this field, mostly only one measuring point was used for the electrical signal, so that no statements could be made about the starting point or the direction of propagation. “We can now say with certainty that the electrical signal originates in the Venus flytrap’s antennae. We see that the signal propagates mainly radially towards the hairs – with no clear direction,” says Linköping University’s Electronic Plants group leader, Eleni Stavrinidou. “Since we can measure signals from the entire trap, we also observe that some signals arise spontaneously and come from sensory hairs that have not been stimulated. This is very interesting and we don’t yet know why this is happening or what the function of it is.”
Similar multi-electrode arrays used by the researchers for the Venus flytrap have previously been used in neuroscience studies in animals. For Stavrinidou, one of the most important aspects of her research is that it shows that bioelectronic technologies, previously used exclusively in biomedicine, can also be applied in plant physiology. “This opens up possibilities for new discoveries,” she explains.