The long-standing mystery of how the Venus flytrap (Dionaea muscipula) can snap shut with astonishing speed, a phenomenon that has puzzled scientists since Charles Darwin, may finally be closer to being understood. New research challenges the widely accepted theory that water movement within the plant's cells is responsible for its rapid closure, instead proposing a mechanism centred on changes in cell wall stiffness.
For decades, it was believed that the Venus flytrap's distinctive trapping mechanism involved water being rapidly pumped from one side of the trap to the other. This movement of water was thought to cause one side of the trap to shrink and the other to swell, generating the necessary curvature to ensnare unsuspecting insects. However, scientists led by Yoël Forterre at Aix-Marseille University in France conducted detailed experiments to test this hypothesis.
Their findings, which have been peer-reviewed, revealed that the time taken for water to move through the trap tissue, both through individual cells and across the plant's structure, was between 30 and 60 seconds. Given that a Venus flytrap typically captures its prey in less than a second, the research team concluded that water transport alone would be far too slow to account for the observed rapid closure. This directly contradicted the prevailing theory and prompted them to seek an alternative explanation.
The researchers then observed that the trap's surface became noticeably bumpier after being triggered. This led them to investigate whether a decrease in cell wall stiffness could be a factor. Using tiny probes to measure the mechanical forces within the epidermal cells, they discovered that upon triggering, the cell walls of the outer epidermal layer rapidly softened. This softening, they propose, releases internal stresses stored in the tissue, allowing pressurised inner cells to expand more on that side. As a result, the outer edges lengthen while the interior surface remains rigid, causing the trap to bend and close.
The team also noted that once the trigger hairs are touched, an electrical signal and a wave of calcium ions are sent across the leaf. These signals act as the plant's equivalent of a nervous system, transmitting information about the touch from the trigger hair to distant cells across the trap within a fraction of a second, initiating the cell wall softening. While this research sheds significant light on the mechanical aspects of the trap's closure, the specific molecules that trigger this rapid cell wall transformation remain unknown, representing the next frontier for investigation.
While the findings offer a compelling new perspective, they are not without debate. Sergey Shabala from the University of Western Australia expressed reservations about the proposed mechanism, suggesting that the assumption of consecutive water movement might be flawed and that changes in cell wall stiffness might take longer than proposed. However, Forterre's team maintains that their direct measurements of tissue swelling times confirm water transport is too slow, contrasting with their measurements showing surprisingly rapid cell wall softening. This new research provides a significant step forward in understanding one of nature's most fascinating biological mechanisms.
Source: Aix-Marseille University