Carnivorous plants, such as the Venus flytrap (Dionaea muscipula), rely on nutrients from small prey animals when growing in nutrient-poor soil. When an unsuspecting prey brushes up against two touch-sensitive hairs on the inside of the trap-shaped leaves, the trap snaps shut, ensnaring the prey for later digestion.
The touch-sensitive hairs, known as trigger hairs, signal trap closure using sodium-activated action potentials (APs). An action potential is a way for cells to send information to one another in the form of an electrical signal. It occurs when positively charged ions, such as sodium, enter a cell and cause the electrical environment of the cell membrane to change until it reaches a certain threshold. After it reaches this threshold the cell “fires,” sending the electrical signal to another cell to activate a response.
In the case of the Venus flytrap, the two trigger hairs send a signal to the leaves to snap shut. Physical stimulation of one hair releases sodium ions into the hair cell, triggering the first action potential. Stimulating a second hair will release more sodium ions, triggering a second AP. Once two APs are elicited within 15-20 seconds of each other, these electrical signals stimulate motor cells in the leaves to snap the trap shut. This signal is incredibly fast, and the trap snaps shut within 100 ms of the triggering of the second hair.
Once the prey is captured it struggles to escape, continuously brushing more trigger hairs that fire more action potentials. These signals are sent to glands that line the leaves, which release enzymes to digest the prey. The prey is loaded with essential nutrients, including sodium, and its digestion provides a source of new sodium ions to trigger the next action potential to capture the plant’s next victim.
To learn more about how the Venus flytrap’s leaves power movement, check out this related strategy.
This strategy was contributed by Alexandra Ralevski.Edit Summary
“The rapid closure of the Venus flytrap (Dionaea muscipula) leaf in about 100 ms is one of the fastest movements in the plant kingdom. This led Darwin to describe the plant as ‘one of the most wonderful in the world’. The trap closure is initiated by the mechanical stimulation of trigger hairs. Previous studies have focused on the biochemical response of the trigger hairs to stimuli and quantified the propagation of action potentials in the leaves.” (Forterre 2005:421).
How the Venus flytrap snapsNatureJanuary 1, 2005
“When an insect visits the trap and tilts the mechanosensors on the inner surface, action potentials (APs) are fired. After a moving object elicits two APs, the trap snaps shut, encaging the victim. Panicking preys repeatedly touch the trigger hairs over the subsequent hours, leading to a hermetically closed trap, which via the gland-based endocrine system is flooded by a prey-decomposing acidic enzyme cocktail” (Böhm et al. 2016:286).
“We have demonstrated that the mechanical energy is received at the multicellular trigger hair and converted into an electrical signal, an AP. The APs originating from the trigger hair on one lobe travel through the entire trap to reach two major targets: (1) the motor tissue, which initiates fast trap closure and the formation of the green stomach, and (2) the glands, the endocrine system responsible for the prolonged processing of the nutrient and sodium-rich animal meal.” (Böhm et al. 2016:291).