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Even the Light Touch of a Green Thumb Slows Plant Growth

Even the slightest touch of plants activates a genetic defence response that, if repeated, slows down plant growth, according to research published in The Plant Journal (

“The lightest touch from a human, animal, insect, or even plants touching each other in the wind, triggers a huge gene response in the plant,” said research leader Prof Jim Whelan of the La Trobe Institute for Agriculture and Food at AgriBio. “Within 30 minutes of being touched, 10% of the plant’s genome is altered.

“This involves a huge expenditure of energy, which is taken away from plant growth. If the touching is repeated, then plant growth is reduced by up to 30%.”

While we don’t yet know why plants react so strongly to touch, the new research findings have led to a deeper understanding of the genetic defence mechanisms involved, opening up new approaches to reducing sensitivity and optimising growth. “We know that when an insect lands on a plant, genes are activated preparing the plant to defend itself against being eaten,” said co-author Dr Yan Wang. “However, insects are also beneficial, so how do plants distinguish between friend and foe?

“Likewise, when plants grow so close together that they touch one another, the retarded growth defence response may optimise access to sunlight. So, for optimal growth, the density of planting can be matched with resource input.”

Whelan said with this deeper understanding of the genetic mechanisms involved, it may be possible to identify and breed plant varieties that are less touch-sensitive while retaining their sensitivity to other factors such as cold and heat.

The research was carried out using thale cress (Arabidopsis thaliana) though it is likely to be applicable to most plants and crops.

The next steps in the research will be to test touch response in crop species and to look at the potential consequences of breeding plants that are less touch-sensitive. “For example, could touch-resistant plants be more susceptible to disease because a crucial defence mechanism has been removed?” Whelan asked.