Researchers at the University of Würzburg, in Germany have shown for the first time that carnivorous Venus flytrap plants (Dionaea muscipula) have the ability to track time between two stimuli 20 seconds apart precisely. This time keeping ability is a remarkable evolutionary adaptation that minimizes false signals that may lead to unnecessary trap closure. Nature is full of random unexpected events and Venus flytrap survival depends on a reliable trigger mechanism for its trap closure. A sensitive trap closing due to false stimuli coming from a falling piece of twig, raindrops or anything other than a juicy insect would be costly.
Dr. Rainer Hedrich, Jennifer Böhm and Sönke Scherzer, from Würzburg, and a team of other scientists demonstrated how Venus flytrap does its time keeping in their research article published in Current Biology.
Venus flytraps live in nitrogen poor soils. They extract much needed nutrients from the insects they trap a pair of modified leaves. On each leaf there are trigger hairs (modified trichomes to be exact). When an insect lands and bumps into trigger hairs on the surface of these leaves, the trap closes. Enzymes secreted into the trap digests the prey. Scientists already knew that trap closure required multiple bumps on the trigger hairs to avoid wasting precious digestive energy. In their research, scientists examined how the plant was responding to movement of the trigger hairs. It turned out that the plant was counting electrical pulses from the trigger hairs.
Trichomes are one of the most adaptive structures in plants. Each trichome is a projection made out of one single cell. They can reflect excess sunlight or even catapult unsuspecting prey into its dewey digestive secretions like in sundew (Drosera) plants.
Role of electrical signals in plant physiology is now increasingly becoming clear. Flowers for example can change their electric field to signal bumblebees for their nectar status manipulating their pollinators behavior. Plants don’t have a nervous system to transmit electrical pulses (action potentials) as animals do. However, biochemically produced action potentials can spread on the surfaces of plant cells.
The researchers artificially tickled the trigger hairs and recorded electrical activity in the plant. The motor cells that close the traps on prey operated only when they received two signals within about 20 seconds apart. The cells in a way started their built-in chronometer with the first signal. After 20 seconds, if no other electrical pulse was generated, the trap naturally disarmed itself.
Immediately after the trap closes, if there is a prey inside, it will freak out and move around like mad. This is when the plant is primed to to digest its prey. More than three flicks of a trigger hair were needed to signal the cells that produce digestive enzymes to begin that process. The more electric signals from the trigger hairs led to secretion of more digestive enzymes. In this way, the flytrap conserves energy and saves precious costly to produce enzymes until they are needed and only in the amount needed.
Adaptations of carnivorous plants to poor soils are fascinating. The tropical pitcher plants for example have been shown to trap ants by changing the slipperiness of their peristomes. The first episode of the series Plants are Cool Too! features the pale pitcher plants. If you would like to learn more about pitcher plants check out an expedition to Palawan island of the Philippines.