Some people have a green thumb, but that doesn’t mean that plants enjoy feeling it. Scientists at La Trobe University have used a common plant research model, Thale Cress (Arabidopsis thaliana), to show that when a plant is repeatedly touched, it can limit the growth of the plant significantly. Even soft touches can trigger massive genetic changes in Thale Cress; the scientists expect that their findings will apply to many types of plants. The results have been reported in The Plant Journal, are outlined in the video, and may help researchers engineer new approaches to plant care and agriculture, from small farms to industrial operations.
Professor Jim Whelan, Research Director of the La Trobe Institute for Agriculture and Food at AgriBio, led the research. He noted that slight touches initiate a defensive response that can slow down the growth of plants when it happens repeatedly.
"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," explained Whelan. "Within thirty minutes of being touched, ten percent 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 thirty percent."
The changes observed by the scientists were in the way genes were expressed; the level of transcripts for genes that function in mitochondrial metabolism and stress pathways were altered, for example.
Study co-author Dr. Yan Wang of La Trobe University added that although we don't know why plants have such a strong reaction to touch, this work has provided us with a deeper understanding of genetic defenses used by plants. That can help us find ways to mitigate plant sensitivity, and promote growth.
"We know that when an insect lands on a plant, genes are activated preparing the plant to defend itself against being eaten," Wang said. "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 defense response may optimize access to sunlight. So, for optimal growth, the density of planting can be matched with resource input."
Whelan noted that the genetic data generated by this work could help identify plant varieties that can be bred to reduce sensitivity to touch while remaining the same in other ways. Now the researchers want to know more about how crop species respond to touch and to assess the potential impact of growing plants that are not as sensitive to being touched.
"As we don't understand why plants display such a strong defense response to touch, if we are to breed less touch-sensitive varieties, we need to first understand what some of the consequences might be," Whelan concluded.
"For example, could touch-resistant plants be more susceptible to disease because a crucial defense mechanism has been removed?"