Plants can sense when something touches them, despite not having nerves

A remarkable study led by Washington State University has unveiled that even in the absence of nerves, plants can perceptively sense touch and its cessation.

This discovery centers around the experiments in which individual plant cells displayed a noticeable reaction to the delicate touch of a fine glass rod. These cells responded by transmitting slow calcium signals to their neighboring cells. 

Fascinating discovery stuns scientists

What’s even more astonishing, upon the release of the pressure, these cells initiated much faster wave patterns. 

While the scientific community has long recognized that plants can react to touch, the novel insight here is that plant cells generate distinct signals when they encounter touch and when it stops.

“It is quite surprising how finely sensitive plants cells are – that they can discriminate when something is touching them. They sense the pressure, and when it is released, they sense the drop in pressure,” said study senior author Professor Michael Knoblauch.

He found it fascinating that plants manage to do this differently than animals, despite the absence of nerve cells and at such an exquisite level.

How the study was conducted

In pursuit of this breakthrough, Knoblauch and his team conducted 84 detailed experiments on 12 plants, specifically on thale cress and tobacco plants. These plants were uniquely bred to incorporate calcium sensors, thanks to modern technology.

The researchers studied pieces of these plants under a microscope, applying a subtle touch to the individual plant cells with a micro-cantilever. This tiny glass rod, almost the size of a human hair, enabled them to witness complex responses, varying with the intensity and duration of the touch. However, the distinction between the touch and its removal was vividly apparent.

Waves instead of nerves

The study revealed that a touch to a cell instigated slow waves of calcium ions, also known as cytosolic calcium. These waves propagated from the touched cell to adjacent cells within 30 seconds, lasting about three to five minutes. Conversely, the removal of the touch spurred an almost immediate set of rapid waves that subsided within a minute.

The researchers attribute these waves to alterations in the cell’s internal pressure. Unlike their animal counterparts, plant cells possess strong cell walls, resistant to permeation. Consequently, even a light touch temporarily increases the pressure within a plant cell.

Confirming the pressure theory

To validate this pressure theory, the team inserted a minuscule glass capillary pressure probe into a plant cell. They found that altering the pressure inside the cell triggered similar calcium waves to those stimulated by the onset and cessation of a touch.

Knoblauch compared this to humans and animals: “Humans and animals sense touch through sensory cells. The mechanism in plants appears to be via this increase or decrease of the internal cell pressure. And it doesn’t matter which cell it is. We humans may need nerve cells, but in plants, any cell on the surface can do this.”

Past research has demonstrated that plants can respond to pests such as caterpillars by activating defensive responses, like releasing chemicals that render leaves less appealing or toxic to the pest. Previous studies also established that brushing a plant incites calcium waves that activate various genes.

The latest study,  published in the journal Nature Plants, takes a step forward by distinguishing between the calcium waves activated by touch and its cessation. 

Many mysteries remain

However, how the plant’s genes react to these signals remains a mystery. With advanced technologies like the calcium sensors utilized in this study, scientists can start unraveling this enigma, according to Knoblauch.

Knoblauch shares his vision for future research: “In future studies, we have to trigger the signal in a different way than has been done before to know what signal, if touch or letting go, triggers downstream events.”

The National Science Foundation financially backed this study. The international collaboration featured researchers from the Technical University of Denmark, Ludwig Maximilian Universitaet Muenchen and Westfaelische Wilhelms-Universitaet Muenster in Germany, the University of Wisconsin-Madison, and of course, Washington State University.

Plants continue to amaze

These findings promise to provide the groundwork for further studies on plant senses and responses. The key lies in exploring diverse methods to stimulate signals and analyze how touch or letting go triggers subsequent events.

While there is much more to discover, this study has significantly broadened our understanding of how plants, despite lacking nerve cells, can sense their environment with a surprising degree of sensitivity. The plant kingdom continues to amaze us with its complex and efficient communication system, which operates in unique and innovative ways compared to animal life.

In a world grappling with ecological challenges, insights into the subtleties of plant behavior could serve as pivotal knowledge for environmental management, agriculture, and conservation. As our understanding of these green beings deepens, it’s clear that there’s more to plants than meets the eye.

The shared endeavor of these international researchers continues to shed light on the remarkable world of plants, ushering in a new era of plant biology and opening up a myriad of potential applications. Indeed, the future of plant science looks promising.

More about plants

Plants are the backbone of all life on Earth and are essential to the survival and well-being of humans in countless ways. They play crucial roles in various ecological functions, including climate regulation, soil conservation, and water cycle maintenance, and they provide a wide array of goods and services directly benefiting humans.

Photosynthesis and Oxygen Production

Through the process of photosynthesis, plants absorb carbon dioxide – a major greenhouse gas – and release oxygen, which is essential for most forms of life, including humans. This process helps regulate atmospheric carbon dioxide levels and contributes significantly to mitigating climate change.

Food Production

Plants serve as the primary food source for humans and other animals. From fruits, vegetables, and grains to the various spices and herbs we use for flavor, almost all of our diet comes directly or indirectly from plants. Moreover, many plants, like legumes, play a critical role in soil fertility by fixing nitrogen from the atmosphere, benefiting other crops.

Medicinal Use

A significant portion of modern medicines are derived from plant extracts. For centuries, various cultures worldwide have utilized a vast array of medicinal plants for treating diseases and promoting overall health.

Ecosystem Services

Plants provide habitat and food for many species, thus supporting biodiversity. They also protect soil from erosion, improve soil quality through organic matter decomposition, and regulate water flow in many landscapes.

Economic Importance

Plants contribute greatly to economies worldwide. Timber, fibers, and many other plant materials are used for housing, furniture, and clothing. Many jobs are tied to the plant-based industries, including agriculture, forestry, and horticulture.

Cultural Significance

Many plants have significant cultural, spiritual, and symbolic value in different societies. They play a crucial role in rituals, ceremonies, and celebrations, and some are considered sacred in various cultures.

Climate Change Mitigation

Forests, in particular, act as carbon sinks, absorbing large amounts of carbon dioxide and storing carbon in their biomass. This function is crucial in the fight against global warming and climate change.

Aesthetics and Mental Health

Gardening and exposure to nature have been shown to have therapeutic effects, reducing stress and promoting mental well-being. Furthermore, plants contribute to the aesthetic appeal of an area, be it a city park, a backyard, or a nature reserve.

Scientific Importance

Plants are important in scientific research and are often used as model organisms in various studies, ranging from genetics to ecology.

To conclude, plants are an essential component of the Earth’s ecosystems and our survival. Our responsibility is to protect and preserve plant life to maintain the health of the planet and ensure the well-being of future generations.

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