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As traps for Venus flies store “memories” of short-term prey

The short-term “memory” of Venus flytrap can last about 30 seconds. If an insect strikes the sensitive hairs of the plant only once, the trap remains motionless. But if the insect strikes again within about half a minute, the leaves of the carnivorous plant close tightly in their prey.

How the traps of Venus (Dionaea muscipula) recall that initial touch was a mystery. A new study reveals that plants do this using calcium, according to online researchers on Oct. 5 in Nature Plants.

Scientists know that some plants have a type of long-term memory, says study co-author Mitsuyasu Hasebe, a biologist at the National Institute of Basic Biology in Okazaki, Japan. An example is vernalization, in which plants remember long periods of winter cold as a sign to bloom in spring. But short-term memory is more enigmatic, and “this is the first direct evidence of calcium involvement,” Hasebe says.

Although the carnivorous plant, famous for its jaw-shaped leaves, has no brain or nervous system, it can apparently count to five and distinguish between live prey and things like rain, which can inadvertently cause its leaves they close and waste energy (SN: 24/01/16). Previous research has suggested that calcium plays a role in this process, but with the help of genetic engineering, Hasebe and colleagues were able to see calcium in action.

After a hair is struck inside a Venus fly trap once, calcium floods the leaf cells, which researchers were able to observe after the plants genetically shone when calcium was present. A second touch, a few seconds after the first, brings more calcium to the cells, brightening the glow and causing the trap to close quickly.

The researchers added genes to Venus's fly traps that produce a protein, which glows green when exposed to calcium. When the equipment touched one of the trap’s sensory hairs, the base of that hair began to glow and then the shine spread across the sheet before it began to fade. When the researchers touched the hair a second time (or touched a different hair on the leaf) in about 30 seconds, the trap leaves lit up even more than before and the plant closed quickly.

The results show that the short-term memory of the fly trap is a depilation and decrease of calcium within the leaf cells, the researchers say. Each time a sensory hair is triggered, it signals the release of calcium. When the calcium concentration reaches a certain level, reached by that second fastest increase in calcium, the trap closes.

Still, research does not reveal all the secrets of the plant. To detect prey, "the fly trap operates a fast electrical network" that can turn a fly or other insect movement into small voltage changes that ripple through plant cells, says co-author Rainer Hedrich, a biophysicist at the University of Würzburg. in Germany. Scientists are still unsure of how the calcium memory system works along with that electrical network to activate plant pressure.

“The close association of calcium and electrical signal is known in common plants, so it was also expected in the Venus fly,” says Andrej Pavlovič, a plant physiologist at Palacký University in Olomouc, Czech Republic, who did not participate in the study. But the most interesting thing about the investigation was getting the trap to shine, he says. These genetic transformations are common in frequently studied plants, but are more difficult to do in less studied predatory plants, so successfully engineered trap genes to make the plant shine "is a big leap forward in studies of carnivorous plants." .

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