Study Reveals a New Trigger in Trapping Mechanisms of Venus Flytraps

The Venus flytrap (Dionaea muscipula) catches spiders and insects by snapping their leaves and traps their prey inside. Venus flytraps are the most well-known carnivorous plant. Its sophisticated trapping system is activated once an unsuspecting prey touches its highly sensitive trigger hairs twice within 30 seconds.

The plant's distinct leaves have three highly sensitive trigger hairs on each love which reacts to the slightest touches by sending out a signal that quickly spreads to the entire leaf. But it snaps within milliseconds once two signals are triggered.

A recent study led by the researchers from the University of Zurich, published in PLOS Biology, showed that a single slow touch also triggers the trap leaves to snap, catching slow-moving larvae and snails.

Slowly Touching the Leaves Triggers Trapping Mechanism

For over 200 years, the physiological reactions of the trapping mechanism of the Venus flytraps have been studied by many experts. These studies all agree that every sufficiently strong touch of a trigger in the leaves could cause an electrical signal. With just two signals within 30 seconds, it could result in the closing of the trap leaves.

But a new study from the University of Zurich (UZH) and ETH Zurich revealed another triggering mechanism for the trap leaves to snap.

According to Ueli Grossniklaus, study co-author and the director of the Department of Plant and Microbiology at UZH, slowly touching a trigger hair only once can also send two signals which lead to the snapping of the trap leaves contrary to the previous studies.

The researchers first determined the forces needed to trigger the trapping mechanism of the plant by using highly sensitive sensors and high-precision microrobotic systems developed by their co-author Bradley J. Nelson, ETH's Institute of Robotics and Intelligent Systems.

The system allowed the researchers to deflect the trigger hairs to a precise angle at a pre-defined speed to measure the relevant forces. The findings of their experiments confirm the previous theory that the trap will snap with two touches of the prey.

Furthermore, the data also were used by researchers at the ETH Institute for Building Materials to develop a mathematical model that will determine the range of angular deflection and velocity threshold that triggers the trapping mechanism of the Venus flytrap.

"Interestingly, the model showed that at slower angular velocities one touch resulted in two electrical signals, such that the trap ought to snap," says Grossniklaus. Subsequently, the researchers were able to confirm the prediction of the model in the experiments.

Venus Flytrap's Way of Catching Slow-Moving Prey

The lobes of the leaves of the Venus flytrap are bent outwards and under strain like a taut spring when it is open. The trap leaves instantaneously snap when the trigger signal leads to even the slightest change in the curvature of the leaves.

Ion channels generate the electrical signals in the cell membrane, which transport atoms out of and into the cell. Researchers think that the ion channels can stay open for as long as the membrane is mechanically stretched.

However, if deflections occur slowly, the flow of ion is enough to send a signal which causes the trap to close, co-first author Hannes Vogler, a plant biologist at UZH explained.

He added that the new trapping mechanism might be a way for Venus flytraps to catch slow-moving prey like the larvae or snails.