It’s Nasty: Thigmonasty (Greek thigma for touch and nastos for pressed close). Closure of the Venus flytrap (Dionaea muscipula), at 40-100 milliseconds, is one of the fastest movements in plant kingdom. Little surprise that it involves action potentials: electrical signals typical of nerve communication in animals. The trap is triggered when at least two of the tiny surface hairs are touched by an insect or spider within 20 seconds of each other. Since the movement costs energy, this coincidence of two stimuli safeguards against waste from accidental triggers.
• There’s no chemistry: Unlike chemical signals, like hormones, action potentials can fire within a millisecond and propagate rapidly over long distances. Although plants have the basic necessities for electrical signaling (ion channels, motor proteins), they have nowhere near the sophistication achieved in animals. Still, an action potential can achieve speeds of up to 40 m/s in plants and is used to respond to environment.
• Touch me: The first step is the opening of mechanically-sensitive ion channels that sense deformity of the hair. This causes the cell membranes to depolarize by reducing the distribution of charges across the cell. If this depolarization exceeds a certain threshold, additional chloride and potassium channels open to let in more ions. Movement of protons makes the cell wall acidic, allowing it to soften and let the cell elongate rapidly. Despite intensive study for ~130 years, the exact mechanism of signaling is not clear.
• Food fight: Recently, the digestive juice of the Venus flytrap was analyzed and found to closely resemble enzymes used in the fight against pathogens, rather than the digestive enzymes of animals. This suggests an evolution from defense pathways to food acquisition in carnivorous plants. Read more: http://www.asbmb.org/News.aspx?id=17935
An early submission for #sciencesunday since I will be traveling tomorrow (Viva Barcelona!).