For a predator to be successful in hunting, it often needs to be faster than its prey.
Plants are not known for their speed.
However, one plant has evolved a quick survival strategy that allows it to feed on insects and spiders that should, by most standards, be safe from their clutches.
We are talking, of course, about the famous Venus flytrap (Dionea muscipula) – a plant that lures prey into a leafy trap, which then closes around the hapless victim, quickly holding it while it digests the plant at its leisure.
Scientists have long puzzled over the mechanism that allows this plant to move faster than plants should.
Now, a team of researchers led by physicist Jeongjun Ryu of the French National Center for Scientific Research (CNRS) says they have identified the culprit.
To activate its jaws, the plant quickly lubricates the cell walls of the trap’s outer skin.
This change allows the outer surface to expand more easily than the inner surface, bending the sheet until it reaches the turning point and closes.
border-frame=”0″ allow=”accelerometer; autoplay; write to clipboard; encrypted media; gyroscope; picture-in-picture; web-sharing” Referrerpolicy=”strict-origin-when-cross-origin”allowfullscreen>“This represents the fastest modification of wall mechanics ever reported in plants.” The researchers write.
“Our findings reveal a pattern of plant movement based on dynamic tuning of material properties, suggesting principles of muscle-free bioactuation.”
Many plants can achieve relatively precise and timely movement. One of the most famous examples appears in Mimosa pudicaor don’t touch me, which folds its symmetrical leaflets when touched, a subtle maneuver thought to help the plant avoid predation or reduce damage from bystanders.
For many plants, these movements are powered by fluid flow, simple hydraulics that change internal pressure and thus the shape of the plant.
Previously, scientists had assumed that the mechanism behind the flytrap’s movements was similarly hydraulic, but that presented a problem.
The traditional hydraulic idea was that the trap closes because water moves from one side of the leaf to the other, causing one side to expand more than the other and bending the trap closed.
Researchers have identified two major flaws in this model.
The first is that water moves relatively slowly through plant tissue. The researchers measured how quickly water moved through a flytrap on Venus, and estimated that it would take between 30 and 150 seconds to move water through the thickness of the trap.
This is too slow for the speed at which the flytrap needs to operate in order to capture its prey.
Certainly, the movements that trigger the closure occur on a time scale of about one second, which is much faster than the water can move through the trap.
Another problem is that the water-driven mechanism must produce a delayed wave of motion through the trap as the water gradually diffuses through the tissue. But the researchers found no sign of such a pattern.
Well, of course the next question is: If not hydraulics, what is?
In their new study, the researchers describe a two-stage abductor process.
The first is the active bending phase, where the trap begins to bend inward toward a critical turning point. The second is the sudden shutdown itself, which takes only 0.2 seconds.
To isolate what initiates the active phase, researchers devised two tests. Initially, the traps were cut into thin strips to obstruct the capture mechanism. Under this condition, the traps were still able to bend, but much more slowly.
In the second test, the traps were opened and fitted with a force sensor to measure the force required to maintain separation between the two lobes. This produced a similar result, revealing a gradual bending motion preceding the rapid twisting phase.
The final piece of the puzzle was observing what the plant actually did during the active bending phase. The researchers used a small probe to measure the rigid cellulose walls of the cells inside and outside the trap before and after closing.
The cell walls on the inner surface barely changed, but those on the outer surface became softer, losing about 40% of their rigidity.
So, here’s how it works.
Before operation, Torgor pressed – The force inside the cell that pushes the cell membrane towards the cell wall – is evenly distributed across the inner and outer walls of the trap.
When a crawling creature triggers the trap by touching one of the sensitive threads inside twice in quick succession, the outer wall softens.
This allows the outer surface to expand more easily than the inner surface, creating a mismatch that causes the sheet to bend.
In a relatively short period of time, this bending exceeds the threshold of sudden instability, and the lobes close, allowing the plant to respond quickly enough to the stimulus to capture a delicious dinner.
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That’s the wild thing, though.
Softening the cell wall is basically how plants grow. The Venus flytrap essentially requested a tool that was already in their genetic pool so they could take a more proactive approach to securing nutrients.
“These subtle adaptations that allow plants to have the upper hand when interacting with animals raise another question – how could they arise from a trial-and-error evolutionary process?” writes bioengineer Jacques Dumais from the Adolfo Ibáñez University of Chile in a related editorial.
We now know how the Venusian flytrap works its magic, but it has not lost its appeal, while those larger evolutionary questions still need to be answered.
The results have been published in sciences.
