Plants react to touch, but also lack of touch

We know that plants react to touch, but now scientists have found a range of responses, including when touching ends.

They communicate with each other via chemical signals and clicking sounds. They can recognise relatives, and enter a kind of hibernation whenever darkness falls.

In recent decades, the secret lives of plants have turned out to be far more sophisticated than ever imagined. And now researchers led by a team from Washington State University have discovered yet another surprising ability of soil-dwelling organisms. During a series of lab experiments, they found that plant cells react both when they are touched – and the moment the touch stops again. We knew from previous studies that plants detect touch and even use the same neurotransmitter as mammals to detect attack and damage. But the new study reveals that cells emit different signals depending on whether the touch begins or ends. “It is surprising that plants can do this – in a very different way than animals, without nerve cells yet at a very high level,” says Michael Knoblauch, lead author of the study. He and his colleagues performed 84 experiments on 12 plants – tobacco plants and the thale cress herb – that had been specially bred with calcium sensors. Specimens of the plants were placed under a microscope while still alive, and the plants were subjected to a very light touch using a thin glass tube around the size of a human hair.

One of the discoveries was that the touch triggered a cavalcade of complex reactions, and that the reactions varied depending on the pressure and duration of the pressure applied.

The researchers could also observe a clear and distinct difference in the plants’ reactions from the time the touch began until it stopped again. During the first 30 seconds after touch, the researchers observed calcium ions travel from the affected plant cell to the surrounding cells in slow waves that lasted 3-5 minutes. But when the researchers removed the thin glass tube again, the plant cells immediately emitted a series of faster waves which receded over a period of one minute.

Having now discovered this new process, the researchers are now planning research to investigate how the signals are affecting the plants.