Australasian Science: Australia's authority on science since 1938

Plants Respond to Touch

Plants can sense and respond to the fall of a raindrop or the touch of an animal, with researchers believing this may enable the plant to defend itself from danger or take advantage of changes in the weather.

Dr Olivier Van Aken of The University of Western Australia said that while nothing visibly happened to plants when they were touched, it launched a cascade of signals inside leaves that prepared them for the future.

The study, published in Plant Physiology (http://tinyurl.com/hhptwqh), reported a change in the expression of thousands of plant genes when plants were sprayed with water. The dramatic response occurred within minutes of spraying and stopped in half an hour.

“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,” Van Aken said.

The researchers could also trigger this response by gently patting the plants or touching them with tweezers. A similar reaction was also elicited by a sudden shadow falling over the plant, limiting their supply of light.

“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,” Van Aken said. “Similar reactions can be triggered by rain drops falling, the wind blowing, an insect moving across a leaf or even by clouds casting a shadow over a plant.

“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.”

The study identified two proteins that help switch off the plant’s touch response. “Switching off the response signal is very important. It allows plants to get on with life as normal, forgetting about the signal and treating it as a false alarm,” Van Aken said.