THE TOUCH RESPONSE

Scientists from the University of Western Australia (UWA) have discovered an intriguing new aspect of plant life that suggests that they respond to touch in one form or another.

Something as simple as water droplets landing on a leaf through to more drastic actions such as patting or touching, can elicit a dramatic response that suggest that plants are highly aware of what is happening to them, according to the UWA scientists’ study published in the Plant Physiology journal.

Lead researcher Dr Olivier Van Aken from the ARC Centre of Excellence in Plant Energy Biology at UWA, said that while there appears to be no visible effect on plants when they were touched, their “touch response” launched a cascade of signals inside leaves that prepared them for the future. The researchers noted how thousands of plant genes expressed themselves differently after being sprayed with water. The dramatic response occurred within minutes of spraying and stopped in half an hour.

Once researchers were able to determine that there were no active compounds in the water that may have triggered the changes, they were able to demonstrate that the plants changed in response to a physical change or stimuli in their external environment.

Researchers pressed forward and examined what other factors could also trigger a response in plants, gently patting the plants or touching them with tweezers. A similar response was also triggered by a sudden shadow falling over the plant, limiting their supply of light. These actions and stimuli produced the same sort of results as the water experiment.  

“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,” explains Dr Van Aken.

 “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”.

Why might plants respond this way? According to research, it appears they may be coordinating their systems to adapt to the need to protect themselves against threats or invasion or even adapting to environmental conditions, such as increased water or light. Dr Van Aken says, “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 findings may cause us to think differently about our interactions with the plants around us. While plants don’t appear to complain when we pinch a flower, step on them or just brush by them while going for a walk, they are fully aware of this contact and are rapidly responding to our treatment of them”.