Plants don’t scream when we step on them or pinch their leaves, but that doesn’t mean they can't feel it.
Researchers have found that when touched, plants launch a ‘touch response’ that sets off a cascade of signals inside their leaves. The study, published in the journal Plant Physiology, suggests that this touch response may prepare a plant to defend itself from danger or deal with changes in the weather.
Initially, the researchers sprayed thale cress, a popular model organism in plant science, with water. A change in expression of thousands of genes occurred within minutes of spraying and stopped a half hour later.
“We were able to show that this response was not caused by any active compounds in the spray but rather by the physical contact caused by water drops landing on the leaf surface,” lead researcher Olivier Van Aken from the ARC Centre of Excellence in Plant Energy Biology at The University of Western Australia said in a press release.
This prompted the researchers to explore what other phenomena might trigger a response in the plants. They found that a similar dramatic response occurred when the plants were gently patted or touched with tweezers, and also when a shadow was cast over them.
In nature, plants are frequently exposed to raindrops, blowing wind, insects moving across leaves, and clouds blocking the sunlight — all of which could prompt the same dramatic responses that were observed in the lab.
“Unlike animals, plants are unable to run away from harmful conditions. Instead, plants appear to have developed intricate stress defence systems to sense their environment and help them detect danger and respond appropriately,” said Van Aken.
He continued: “Although people generally assume plants don’t feel when they are being touched, this shows that they are actually very sensitive to it and can redirect gene expression, defence and potentially their metabolism because of it.”
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