The intriguing mechanism behind how Venus flytraps close quickly to ensnare insect prey has seen substantial investigation.

The Venus flytrap (Dionaea muscipula) reacts instantly when its sensitive hairs are stimulated twice, leading to a swift trap closure. This plant is known for its ability to capture various insects, including a tiny frog. However, the exact workings of this fascinating process have remained elusive to scientists since the days of Charles Darwin.

Many experts believe that the closure mechanism involves a rapid transfer of water through the trap’s tissues, causing one side to contract while the other expands, thereby facilitating the quick closure. To test this theory, Yoel Forterre and a team from the University of Aix-Marseille, France, investigated the water’s transit time across both isolated cells and tissue in the trap.

They found that water movement took approximately 30 to 60 seconds, leading researchers to conclude that this mechanism would be too slow, as trap closure typically occurs within a second.

Subsequently, researchers observed that the trap’s surface texture changed to a bumpier state after activation, indicating a reduction in cell wall stiffness. They employed fine probes to measure mechanical forces within the epidermal cells to examine if this softening contributed to the trap’s closure.

“When the trap is stimulated, we found that the outer epidermal layer’s cell walls softened almost instantaneously,” stated Forterre. Upon triggering the hairs, electrical signals and waves of calcium ions travel throughout the leaf. He likened these signals to the plant’s version of neural impulses, enabling rapid communication regarding the touch contact from the trigger hairs to distant cells within moments.

Upon receiving these signals, the outer surface of the trap quickly decreases in mechanical stiffness, releasing internal stress and allowing pressurized inner cells to contract further on one side. Consequently, the outer edge expands while the inner surface remains hard, bending the trap shut.

Despite these findings, researchers still lack clarity on the specific molecules responsible for these swift changes in cell wall dynamics. “We grasp the initial sensing mechanism and the final trapping movement, but understanding the molecular connections between these events remains elusive,” emphasized Forterre.

Professor Sergei Shabara from the University of Western Australia expressed skepticism about the proposed mechanism, arguing that water might not flow continuously through the cells as suggested. He believes cell wall stiffness adaptations could take several minutes instead of being instantaneous. “Although the methodology of this study is impressive, it does not definitively rule out water movement as a driving force,” stated Shabara.

Nevertheless, Forterre highlighted that their measurements regarding tissue swelling time support the idea that water transport across the trap is too slow to account for rapid closure, emphasizing the unexpectedly swift decrease in cell wall stiffness.