Scientists reveal the secret behind the carnivorous plant's closing mechanism

Poor thing about the fly that lands on a Venus flytrap. When the insect touches the hair-like structures of this remarkable carnivorous plant, its trap closes, condemning the victim to be digested over several days by secreted enzymes. Scientists have now discovered the physical mechanism behind this sudden closure.

Researchers said experiments have shown that closure of the Venus flytrap is initiated by a rapid softening of the cell walls in the outer layer of the Venus flytrap, which is a highly modified leaf divided into two hinged lobes that resemble toothed jaws.

For more than a century, the prevailing hypothesis was that trap closure was driven by a rapid redistribution of water within the leaf, with water moving between cells to swell one side of the leaf. The new research points to a different biological mechanism.

"One of the world's most iconic plants still manages to surprise us. After more than a century of research, we continue to discover fundamentally new things about how the carnivorous plant Venus works," said physicist Yoël Forterre, from the CNRS (French National Center for Scientific Research) and the University of Aix-Marseille, lead author of the study published on Thursday in the journal Science.

The Venus flytrap (or carnivorous plant of the genus Venus flytrap) is a small carnivorous plant native to a restricted region of North Carolina and South Carolina, in the United States. Like many carnivorous plants, it grows in nutrient-poor environments and supplements its nutrition by capturing and digesting insects.

In experiments conducted in Marseille, researchers used high-speed imaging, mechanical measurements by indentation of the plant's outer layer and mechanical modeling. They also measured water transport within plant tissue to rule out this possibility as a mechanism involved.

"The plant uses specialized sensitive hairs located on the inner surface of the trap. When an insect touches these hairs twice in a short period of time, the trap closes. Closing can occur in just a tenth of a second," Forterre said.

"Our hypothesis is that the trap is already mechanically loaded before it is triggered, similar to a spring. When the trap is stimulated, the cell walls of the outer epidermal layer quickly soften by about 30 to 40%, meaning the cell wall becomes more flexible. This releases internal tensions stored in the tissue and causes the trap to fold and close. Softening occurs in about a second," Forterre said.

When the trap closes, the insect is sealed inside to be digested.

"By directly measuring the mechanics of the live trap as it responds, we identify the internal 'motor' that drives the leaf beyond its instability threshold and triggers the sudden closure that closes it," said physicist and lead author of the study Jeongeun Ryu, who worked on the study as a postdoctoral researcher at CNRS and Aix-Marseille University.

After the plant absorbs the nutrient-rich liquid produced by the digestive processes, the trap reopens, leaving behind the insect's empty exoskeleton.

"What I find remarkable is that evolution often does not invent entirely new mechanisms, but rather reuses and improves existing ones. Plants are known to modify the mechanical properties of their cell walls during growth, but the Venus flytrap appears to take this mechanism to the extreme, using it on a time scale of about a second," Forterre said.

There are approximately 800 known species of carnivorous plants. They are not all closely related, which indicates that meat-eating evolved independently several times during plant evolution.

The closing mechanism of the Venus flytrap is a topic that has long interested scientists, including Charles Darwin, the 19th-century naturalist who developed the theory of evolution by natural selection. The researchers envision potential practical applications of their findings.

"To our knowledge, this is the first time that such a rapid change in the mechanical properties of cell walls has been observed in a plant," Ryu said.

"This solves a question that goes back to Darwin - what drives one of the fastest movements in the plant kingdom - and points to a new way for a living thing to move: not by pumping fluid or simply collapsing, but by actively adjusting the stiffness of its own material. This principle could eventually inspire flexible robots or smart materials, although this remains a long-term prospect," Ryu said.

Source: CNN