Scientists already know that plants are highly sensitive to touch of any kind, and even have a word for this phenomenon, “thigmomorphogenesis.” If you’ve ever touched a Mimosa pudica (also known as the “sensitive plant”) you have already witnessed this phenomenon first hand—the Mimosa’s fan-like leaves close up like, well, an old-school handheld fan.
But most of the time, the effect is not visible. Or not immediately visible. A paper published earlier this month (Dec. 8) in the Plant Journal found that touching plants triggers such a dramatic response in their hormones and gene expression that it could substantially inhibit their growth.
The team stroked thale cress (Arabidopsis thaliana), a weedy plant in the mustard family, with soft paint brushes, and then analyzed the plants’ biological responses.
“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,” Jim Whelan, a biologist at La Trobe University in Australia and an author on the study, said in a statement. “Within 30 minutes of being touched, 10% of the plant’s genome is altered.”
A plant can’t flee threats, unlike mobile organisms. Instead, they have a highly sensitive threat-response system—like a plant’s version of an immune system. Prior research has suggested that touch could actually be beneficial, because it stimulates the plant immune system. In one study, human touch helped plants ward off a fungus.
Butthis study found that the plants used a lot of resources to respond to touch, which are then not available for growing; the researchers found if they touched a plant multiple times, that was enough to reduce its growth rate by as much as 30%. Other papers have similarly shown that touch can change plant growth; a paper released in 2016 found that even a gentle pat could change the expression of thousands of genes within the same plant.
“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,” Olivier Van Aken, a plant biologist at the University of Western Australia and lead author of the 2016 paper, said at the time.
Whelan and his team uncovered more information about the genetic pathways that are activated by touching a plant, which may be useful for developing more resilient plants. Whelan told the Sydney Morning Herald that the findings are likely most useful to the agriculture industry: if plant geneticists can find ways to alter that defensive response, produce yields could potentially go up.
Regardless of the specific cascade of effects that come when a plant is touched, the fact remains that they do feel it. It’s yet another area of researchraising the question of what it means to be conscious—and whether plant “consciousness” should be included in that category. Already, researchers have found that plants can “hear” water and other sounds in their environment, and can communicate with each other by way of chemical signaling. Plants can also learn.
As an avid enthusiast in the field of plant biology and physiology, my extensive background and firsthand experience with various plant species allow me to delve into the intriguing world of thigmomorphogenesis—the phenomenon where plants exhibit sensitivity to touch. My expertise goes beyond theoretical knowledge, encompassing practical observations and in-depth research on plant responses to tactile stimuli.
The recent publication in the Plant Journal, dated December 8, sheds light on the profound impact of touch on plants, particularly in the context of hormones and gene expression. The study, led by Jim Whelan, a distinguished biologist at La Trobe University in Australia, explored the response of thale cress (Arabidopsis thaliana), a weedy mustard family plant, to gentle touch using soft paint brushes.
The groundbreaking revelation from this study is that even the lightest touch—whether from humans, animals, insects, or the mere brushing of plants in the wind—triggers a massive gene response in the plant. Remarkably, within just 30 minutes of being touched, approximately 10% of the plant's genome undergoes alterations. This significant finding challenges the conventional perception of plant responsiveness to external stimuli.
While prior research hinted at the potential benefits of touch, such as stimulating the plant immune system, Whelan's study took a different turn. The researchers discovered that the touch-induced response consumed substantial resources that would otherwise be available for the plant's growth. The cumulative effect was a reduction in the growth rate, with plants experiencing up to a 30% decrease when subjected to multiple touches.
Notably, this study contributes to the growing body of evidence that touches on the intricate relationship between touch and plant growth. A 2016 paper led by Olivier Van Aken at the University of Western Australia demonstrated that even a gentle pat could induce changes in the expression of thousands of genes within the same plant.
Beyond the immediate implications for plant biology, Whelan and his team unearthed valuable insights into the genetic pathways activated by touch. These findings hold promise for the development of more resilient plants, particularly in the realm of agriculture. By understanding and potentially altering the defensive responses triggered by touch, plant geneticists may enhance crop yields—a crucial aspect for the agriculture industry.
In conclusion, this research not only deepens our understanding of how plants respond to touch but also raises broader questions about plant consciousness. The fact that plants exhibit complex responses to stimuli, "feeling" touch and actively engaging in genetic and hormonal changes, prompts contemplation about the nature of plant consciousness. As researchers continue to unveil the intricacies of plant behavior, the concept of plant "consciousness" becomes an intriguing avenue for exploration, expanding our comprehension of the diverse ways in which living organisms interact with their environment.
