Describe the rapid response of the Venus fly trap to stimulation of hairs on the lobes of modified leaves and explain how the closure of the trap is achieved

Sourav PanNovember 1, 2024

Answered

Rapid Response to Stimulation:

1. Triggering Event: When an insect touches one of the sensitive trigger hairs on the inner surface of the Venus flytrap’s modified leaves (lobes), it stimulates the cells at the base of the hair.
2. Electrical Signal Generation: This mechanical stimulation activates mechanosensitive ion channels, generating receptor potentials that induce an action potential (AP). This electrical signal is propagated between the lobe and the midrib.
3. Charge Accumulation: The Venus flytrap can accumulate small, subthreshold electrical charges. If a second trigger hair is touched within a specific time frame (approximately 20-30 seconds), the accumulated charge reaches a threshold value.
4. Rapid Closure: Upon reaching the threshold, the trap closes rapidly, snapping shut in about 0.3 seconds. This speed is consistent regardless of whether the stimulation is mechanical (e.g., touching trigger hairs) or electrical (e.g., injecting a specific electrical charge, approximately 14 μC).

Mechanism of Trap Closure:

1. Change in Cell Turgor Pressure: The rapid closure is primarily driven by a sudden change in turgor pressure within the leaf cells.
2. Water Movement: The electrical signal triggers the rapid movement of water from cells on the outer surface of the leaf to cells on the inner surface.
3. Leaf Folding: This redistribution of water causes the leaf to fold inward rapidly, with the two lobes of the modified leaf closing together to trap the prey.
4. Sealing and Digestion: Once closed, the trap seals, and the Venus flytrap secretes digestive enzymes to break down the trapped insect, allowing the plant to extract essential nutrients.

Underlying Principles:

• Electrical Memory: The Venus flytrap exhibits a form of electrical memory, allowing it to accumulate subthreshold stimuli until a threshold is reached, ensuring that closure is not triggered by single, potentially false, stimuli (like raindrops).
• Mechanosensing: The trigger hairs act as micronewton mechano-sensors, capable of detecting the small movements associated with insect prey, thereby initiating the capture process.