A recent study led by Washington State University has revealed that plants possess the ability to sense touch and pressure, even in the absence of nerves. Through a series of experiments, researchers discovered that individual plant cells generate slow waves of calcium signals to neighboring cells when touched with a fine glass rod, and these signals transition to rapid waves upon the release of pressure. This study sheds light on how plants perceive touch and highlights the remarkable sensitivity of plant cells.
The experiments involved 84 trials on 12 plants, including thale cress and tobacco plants engineered to incorporate calcium sensors. Under a microscope, the researchers applied gentle touches to individual plant cells using a micro-cantilever, observing diverse responses dependent on the force and duration of the touch. Notably, the distinction between touch initiation and release was evident. Within 30 seconds of the touch, slow waves of calcium ions, known as cytosolic calcium, propagated from the stimulated cell to neighboring cells, persisting for approximately three to five minutes. Conversely, the removal of the touch triggered rapid waves that dissipated within a minute.
The observed waves are believed to be a response to changes in pressure within plant cells. Unlike animal cells, plant cells possess rigid cell walls that cannot be easily penetrated. Consequently, even a gentle touch temporarily increases pressure within a plant cell. To confirm the pressure hypothesis, the researchers mechanically manipulated cell pressure using a small glass probe, resulting in similar calcium waves when pressure was increased or decreased, mimicking the start and stop of touch.
This research contributes to our understanding of how plants perceive and respond to touch, offering insights into their defense mechanisms against pests and environmental stimuli. Previous studies have shown that pests biting plant leaves can trigger defensive responses, such as the release of chemicals that deter or harm the pests. Brushing a plant has also been found to initiate calcium waves that activate specific genes.
While this study successfully distinguished between touch and release signals, further investigation is needed to unravel how these signals translate into specific genetic responses within plants. Advancements in technologies like calcium sensors enable scientists to delve deeper into this mystery. Future studies aim to explore alternative methods of triggering signals and deciphering the downstream events initiated by touch or release.
Supported by grants from the National Science Foundation, the study involved an international team of researchers from institutions such as the Technical University of Denmark, Ludwig Maximilian Universitaet Muenchen, Westfaelische Wilhelms-Universitaet Muenster in Germany, University of Wisconsin-Madison, and Washington State University.
