Carnivorous plants like the Venus flytrap obtain their nourishment by luring insects with a fruity scent and then using a hair-trigger to catch their prey, but scientists have long wondered just how they can tell when the time is right to spring their trap. As it turns out, they count.
As Sci-news.com and Science World Report reported recently, a team of researchers led by Dr. Rainer Hedrich, a biologist at Universität Würzburg in Germany, tried to fool Venus flytraps into thinking that they had attracted insects by applying mechano-electric stimuli to their traps.
They found that a single touch to the trap’s trigger hair caused the plant to set its trap to a “ready-to-go mode,” but did not cause it to spring. A second touch caused the trap to engulf the prey and begin the digestive process. As an insect attempts to escape, it would repeatedly touch the trigger hairs, causing the plant to become increasingly excited, according to the study authors.
At this point, the plant would then begin to produce a special touch hormone, and after receiving five triggers, glands on the trap’s inner surface would start to produce digestive enzymes, as well as special transporters to collect nutrients from its victim. In a statement, Dr. Hedrich called it a “deadly spiral of capture and disintegration.”
Number of stimulations trigger different digestive responses
Researchers knew that when an insect visited a Venus flytrap’s snare and then touched its trigger hair, it would cause the plant to fire what are known as action potentials or APs. After two of the APs are triggered by a moving object, the snap trapped shut, capturing the prey.
In their new study, published in the journal Current Biology, Dr. Hedrich and his fellow researchers set out to discover just how many times the trigger hairs needed to be stimulated, and how many APs must be emitted, before the plant recognized that it had indeed trapped food.
“The number of action potentials informs [the plant] about the size and nutrient content of the struggling prey. This allows the Venus flytrap to balance the cost and benefit of hunting,” said Dr. Hedrich. His team found that two stimuli are needed to activate the touch hormone jasmonic acid-signaling pathway, while at least three are required to trigger the expression of genes which encode prey-degrading hydrolases.
If a Venus flytrap receives more than three stimulations, it ramps up the production of digestive enzymes to deal with what is likely larger prey, the researchers said, and the entire process also revealed a significant increase in the production of a substance which allows the plant to gather sodium from its victims. It is not clear at this point how the flytrap benefits from that salt, but it may have something to do with maintaining water balance in its cell walls, the authors said.
Dr. Hedrich’s team is now in the process of sequencing the genome of the Venus flytrap, and are hopeful that they will gain new insights into the chemistry and sensory system of the carnivorous plant through this research. Potentially, decoding the species’ DNA could provide clues into how the mechanisms it uses to digest its prey developed and evolved over time.
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