This article originally appeared in Meta Science News January 2016
Although it is actually a flowering perennial, the Venus flytrap is better known for its carnivorous diet. Scientists have long known that electrical signals trigger a string of events that trap and digest the prey, but it is an energy expensive proposition for a plant in a nutrient-poor habitat. Researchers looked further into the mechanisms and the payout for capturing prey. First author Jennifer Böhm and colleagues at the Institute for Molecular Plant Physiology and Biophysics (Würzburg) reported their findings today in Current Biology.
Venus flytrap leaf endings are bilobed capture organs able to sense and enclose prey. They are lined with sensitive trigger hairs that are stimulated by touch and generate action potentials (AP). “Touch, a mechanical stimulus is converted by the trigger hair into an electrical wave. Two touches stimulate the lobes to close,” the researcher said in the video abstract.
As the trapped insect struggles to escape, it unwittingly continues to stimulate the plant, which sets off a chain of activities. The bilobes, lined with glands that can secrete acids and digestive enzymes, close into a green stomach. The researchers wondered how many triggers are needed to identify the encaged object as food and therefore make it worthwhile to activate the glands.
To learn more, they harvested capture organs that were repetitively stimulated and analyzed its genetic material. “The molecular analysis shows that from the second action potential is [turned] on, touch hormones are being activated. Touch hormones induce the production of digestive enzymes,” they said in the video abstract.
The researchers tracked the number of trigger-hair stimulations. They found that the touch hormone jasmonic acid signaling pathway is activated after the second stimulus.
“…More than 3 APs are required to trigger an expression of genes, encoding prey-degrading hydrolases, and that expression is proportional to the number of mechanical stimulations,” noted the authors. This helps the plant breakdown the meal.
Insects are rich in several nutrients, but especially potassium and sodium. The researchers also took a close look at the uptake of these nutrients. Their evidence points to a system designed to take in sodium.
Trapped insects constitute a rich source of sodium. Image from Böhm et al.
“We identified a flytrap sodium channel DmHKT1 as responsible for this sodium acquisition, with the number of transcripts expressed being dependent on the number of mechano-electric stimulations,” the authors say. By eliciting between 5 and 60 APs, the expression of DmHKT1 increased up to 60-fold.
Put another way, a wriggling, captured insect intent on escape instead informs the Venus flytrap that a sodium-rich dinner has been served.
Kimberly Hatfield | Meta Staff Writer
Featured image: The red dots are glands. When the trap closes, forming a green stomach, these glands release a lytic enzyme cocktail, digest the victim, and incorporate the nutrients release from the building blocks of the meat. Credit: Sönke Scherzer