Venus flytraps are capable of detecting the movements of even the smallest insects. This mechanism protects the plant against starving from hyperactivity as a new study conducted by scientists from Würzburg and Cambridge reveals.
Physically bound to a specific location, plants have to devise special ways to secure their supply of vital nutrients. Most plants have developed a root system to the nutrients they need in order to survive out of the soil.
But what if nutrient-poor soils fail to provide the necessities of life? Carnivorous plants such as the Venus flytrap have found a way out of this dilemma.
The Venus flytrap is native to the wetlands of North and South Carolina on the East Coast of the USA. Instead of taking in nutrients through its roots alone, the carnivorous plant traps prey within its leaves that can snap shut within a fraction of a second.
The plant is capable of sensing prey through delicate trigger hairs on the inside of its flat leaves. Since prey insects come in different sizes and the Venus flytrap cannot afford to be fussy, the plant grows traps across a variety of sizes.
Now researchers from the universities of Würzburg and Cambridge have discovered that the tactile sensors in these traps already respond to minute pressure stimuli, converting them to electrical signals that cause the trap to close. They have published their results in the current issue of Nature Plants.
Trigger hair converts touch into electricity
"Each trap lobe features three to four multicellular hairs which are torsion-resistant except for a notch at the base. When an insect, lured by the smell, colour or nectar of the trap, touches the trigger hair, the hair will yield in the area of the non-reinforced base. This causes the sensory cells in this area to be stretched on one side and compressed on the other side," says Professor Rainer Hedrich, explaining the operating principle of the Venus flytrap.
The biophysicist and plant researcher, who holds the Chair of Botany I at the University of Würzburg, has been studying the carnivorous plant species for some time.
When the sensory cells are deformed in this way, the tactile sensors respond by converting mechanical energy into electrical signals, triggering an action potential, which rapidly propagates from the base of the trigger hair throughout the entire trap. When a trigger hair is touched a second time within a short time period, the process is restarted – and only then does the trap close.
But how much does an insect deflect the trigger hair? What is the minimum size and weight that an insect must have in order to be detected by the Venus flytrap? Professor Hedrich had these questions in mind when conducting his latest study. "It was clear from the beginning that we would not easily get the answers using flying insects," Professor Hedrich explains.
So when looking for a suitable insect prey to use in their experiments, Professor Hedrich and his team opted for ants. Professor Walter Federle, a biomechanics expert and ant specialist at the University of Cambridge, provided the necessary expertise and support for the experiments of the Würzburg plant scientists.
Minimal deflection triggers electrical stimulation
How can ants be made to touch a trigger hair on command? To solve this problem, ant specialist Federle chose leaf-cutting ants. This ant species regularly commutes between the foraging site and the nest. For the experiment, Federle mounted single-trap lobes within the foraging trail of a leaf-cutting ant colony.
He then monitored the ant traffic on the flytrap trail using a high-speed camera that recorded all contacts. The result: Federle's analysis yielded a minimum and maximum trigger hair deflection of 3.5 and 7.5 degrees, respectively.
Now in order to determine the angle and force necessary to trigger an action potential in the Venus flytrap, the scientists replaced the ants with computer-controlled micro-manipulators equipped with special force transducers. After the micro-manipulators had been deposited on the trigger hairs, the deflection angle was varied progressively.
"We were surprised to find that our voltage detectors already recorded an action potential at a deflection of around 2.9 degrees," says Dr Sönke Scherzer, lead author of the study and a scientist in Professor Hedrich's department. This means that the Venus flytrap already detects the weakest contact with a leaf-cutting ant.
A trap for each fly size
An ant or housefly creates a force when walking which is approximately equivalent to its body weight. So a fly weighing ten milligrams is capable of generating 100 micronewtons, a force that is easily sufficient to excite a large trap. However, if a mosquito weighing just three milligrams ends up in such a large trap, the trigger hairs will not be deflected.
But since a mosquito, too, can be an important source of nutrients, the Venus flytrap has also developed smaller traps during the course of evolution. These mini-traps also respond to the smaller forces generated by the lightweight mosquito.
"This trap-size-based sensitivity of the trigger hairs is crucial for the economic efficiency of the traps," Professor Hedrich explains. After all, it costs the plant much more energy to reopen a large trap than a small one. "If underweight, low-nutrient prey insects were able to trigger large traps, the cost-benefit ratio would turn out negative and the Venus flytrap would slowly starve in the worst case," Professor Hedrich explains.
When trigger hairs get weary
Once the trap has closed, the insect prey usually does not just accept its fate. Instead it struggles and tries to escape. In its panic, it constantly touches the tactile hairs, triggering up to 100 action potentials in two hours. According to Professor Hedrich, the Venus flytrap takes into account these electrical signals and initiates a corresponding response that ranges from the production and excretion of digestive enzymes to taking up the nutrients from the decomposed prey.
The scientists conducted another experiment to determine how often a single trigger hair can be stimulated within one hour. The result: "From a frequency of a tenth of a hertz, that is one stimulation every ten seconds, the trigger hair starts to exhibit signs of fatigue," says Sönke Scherzer.
At higher frequencies, an action potential was no longer triggered each time a tactile hair is stimulated and eventually the electrical events did not take place at all. When the scientists interrupted the repeated stimulation sequence for a minute, the hair fully regained its mechano-electrical properties.
Sensory cells under the microscope
To build on this research, the researchers aim to find out how the flytrap counts and why the tactile hair stops responding when stimulated at high frequency. For this purpose, they will isolate the trigger hairs and sensory cells and determine a number of properties such as the fatigue and recovery of the ion channels that convert the tactile stimulus to an electrical event.
Prof. Dr. Rainer Hedrich, Department of Botany I (Plant Physiology and Biophysics) of the University of Würzburg, T: +49 931 31-86100, email@example.com
Venus flytrap trigger hairs are micronewton mechano-sensors that can detect small insect prey, S. Scherzer, W. Federle, K. A. S. Al-Rasheid and R. Hedrich. Nature Plants, DOI: 10.1038/s41477-019-0465-1. https://www.nature.com/articles/s41477-019-0465-1.
Gunnar Bartsch | Julius-Maximilians-Universität Würzburg
New self-assembled monolayer is resistant to air
22.01.2020 | University of Groningen
Mosquitoes are drawn to flowers as much as people -- and now scientists know why
22.01.2020 | University of Washington
A Duke University research team has identified a new function of a gene called huntingtin, a mutation of which underlies the progressive neurodegenerative...
For years, a new synthesis method has been developed at TU Wien (Vienna) to unlock the secrets of "strange metals". Now a breakthrough has been achieved. The results have been published in "Science".
Superconductors allow electrical current to flow without any resistance - but only below a certain critical temperature. Many materials have to be cooled down...
KIT researchers develop novel composites of DNA, silica particles, and carbon nanotubes -- Properties can be tailored to various applications
Using DNA, smallest silica particles, and carbon nanotubes, researchers of Karlsruhe Institute of Technology (KIT) developed novel programmable materials....
Styrofoam or copper - both materials have very different properties with regard to their ability to conduct heat. Scientists at the Max Planck Institute for Polymer Research (MPI-P) in Mainz and the University of Bayreuth have now jointly developed and characterized a novel, extremely thin and transparent material that has different thermal conduction properties depending on the direction. While it can conduct heat extremely well in one direction, it shows good thermal insulation in the other direction.
Thermal insulation and thermal conduction play a crucial role in our everyday lives - from computer processors, where it is important to dissipate heat as...
In order to advance the transfer of research developments from the field of quantum sensor technology into industrial applications, an application laboratory is being established at Fraunhofer IAF. This will enable interested companies and especially regional SMEs and start-ups to evaluate the innovation potential of quantum sensors for their specific requirements. Both the state of Baden-Württemberg and the Fraunhofer-Gesellschaft are supporting the four-year project with one million euros each.
The application laboratory is being set up as part of the Fraunhofer lighthouse project »QMag«, short for quantum magnetometry. In this project, researchers...
16.01.2020 | Event News
15.01.2020 | Event News
07.01.2020 | Event News
22.01.2020 | Life Sciences
22.01.2020 | Power and Electrical Engineering
22.01.2020 | Life Sciences