The Venus Flytrap Pressure Sensor

All plant cells can be made to react by touching or hurting them. The carnivorous Venus flytrap (Dionaea muscipula) has very sensitive organs for this purpose: sensory hairs that register even the weakest mechanical stimuli, amplify them, and convert them into electrical signals that then spread rapidly through plant tissue.

Researchers from Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, have isolated individual sensory hairs and analyzed the gene pool active in insect trapping. “In the process, we found for the first time genes that presumably serve throughout the plant kingdom to convert local mechanical stimuli into systemic signals,” says Professor Rainer Hedrich, a plant researcher at JMU.

That’s good, because virtually nothing was known about mechanoreceptors in plants until now. Hedrich’s team presents the results in the open access journal PLOS Biology.

Sensory hairs turn touch into electricity

Dionaea’s hinged trap consists of two halves, each with three sensory hairs. When a hair bends to the touch, an electrical signal, an action potential, is generated at its base. At the base of the hair there are cells in which the ion channels open due to the stretching of the surrounding membrane and become electrically conductive. The upper part of the sensory hair acts as a lever that amplifies the stimulus unleashed by even the lightest prey.

These micro-force-touch sensors thus transform the mechanical stimulus into an electrical signal that extends from the hair throughout the fin trap. After two action potentials, the trap snaps shut. Based on the number of action potentials unleashed by the prey during its attempts to free itself, the carnivorous plant estimates whether the prey is large enough, whether the elaborate digestion is worth setting in motion.

From genes to touch sensor function

To investigate the molecular basis for this unique function, Hedrich’s team ‘harvested’ around 1,000 sensory hairs. Together with Professor Jörg Schultz, a bioinformatician at JMU, they set out to identify the genes in the hairs.

“In the process, we noticed that the fingerprint of the active genes in the hair differs from that of the other cell types in the trap,” says Schulz. How is mechanical stimulus converted to electricity? “To answer this, we focused on ion channels that are expressed in sensory hair or found exclusively there,” says Hedrich.

In search of more ion channels

The hair sensory-specific potassium channel KDM1 was highlighted. Newly developed electrophysiological methods showed that without this channel, the electrical excitability of sensory hairs is lost, that is, they can no longer fire action potentials. “Now we need to identify and characterize the ion channels that play an important role in the early stages of the action potential,” Hedrich said.