Many animals eat plants, but few plants eat animals. If the first scenario is the most normal, the second still involves some mysteries even for scientists. How could plant know-how or when to eat an animal?
In the case of the Venus Flytrap, one of the most popular and fascinating carnivorous plants in the world, this process is only a matter of time. Whether you’re a fly, spider, beetle or grasshopper, time is a key aspect if you don’t want to become their lunch.
What happens is that for the Venus flytrap to gobble up the animal always requires two successive stimuli to take place before. Sensory hairs inside their jaws need to perceive their prey twice, and both contacts should normally occur with a maximum difference of 30 seconds.
If the period between the first touch and the second touch lasts more than 30 seconds, the flytrap sets the counter to zero. And here comes a question: How does a brainless plant remember something and how does it know when these 30 seconds expire?
Scientists came close to responding to this unknown about 30 years ago, the journal Nature Plants writes. At the time, German researchers assumed that the closing of jaws of this carnivorous plant caused it by an increase in calcium ions in the plant. These two successive sensory contacts may be increasing calcium concentration. The increase in the level of this, they assumed, was what caused the closing of jaws.
A study published in @NaturePlants visualizes intracellular calcium concentrations in the Venus flytrap and demonstrates that its short-term memory can be explained by changes in calcium concentration. https://t.co/E7X2vZwXnO pic.twitter.com/Uhu9UQbb9c
— Nature Research (@nresearchnews) October 11, 2020
In the new study, led by biologist Mitsuyasu Hasebe of Japan’s National Institute of Basic Biology, researchers found out a way to visualize intracellular calcium concentrations within the plant to see if the chemical gave the plant the ability to remember and forget.
Using a bacterium called Agrobacterium— capable of transferring genes to plants— researchers designed transgenic fly-hunters from the Venus flytrap equipped with a calcium sensor, a protein called GCaMP6, which emits green fluorescence when it joins calcium.
The plant shines brighter every time its sensor hairs feel something. In the wild, this visual change could alert the prey to the threat of being gobbled up.
During these experiments, researchers observed that when touching the sensory hairs for the first time the plant began to shine almost instantly, with a fluorescence wave that extended outwards throughout the rest of the plant and was accompanied by a temporary increase in calcium.
“Electrical excitation of the trap cells thus causes an increase in calcium concentration,” explained lead author and biophysicist Rainer Hedrich from the University of Würzburg in Germany.
“If it is stimulated again, its calcium value is added to the first signal,” says the scientist. With the help of calcium, the Venus flytrap can count the number of times its prey touches it.
If it is not stimulated again within approximately 30 seconds, the intracellular calcium concentration dissipates and instructs the plant not to intervene.
In 2016, the president of the Argentine Association of Carnivorous Plants, Federico Parrilli, explained that these plants are not dangerous to humans.
“None of them have thorns, nor is it poisonous, or anything that can cause any physical harm to humans or pets, unless the pet is a fly,” he joked.
Venus flytrap, or Dionaea muscipula, native to the southeastern United States, is the only species in the monotypic genus Dionaea, a carnivorous plant in the Droseraceae family. The name of this plant refers to its eating habit of catching live prey, usually insects and arachnids.