Researchers at theShenzhen University of Advanced Technology and University of Würzburg have discovered that plants communicate root injuries within milliseconds via mechanical signals. A sudden drop in hydraulic pressure serves as an ultra-fast alarm system for neighboring roots'defense. The groundbreaking findings of this study have been published in the renowned journal Science Advances.

When plant roots are injured—for instance, byforaging insects—their internal hydraulic pressure collapses immediately.This physical pressure wave propagates at high speed throughout the entire root system. In neighboring, still-intact roots, tiny membrane proteins acting as mechanical pressure sensors detect the mechanical stress and instantly translate it into electrical and calcium signals. But how exactly do roots translate mechanical stress into a targeted defense response?

The study was led by Rainer Hedrich,Chair Professor at SUAT, and Dr. AngelBaudon, a postdoctoral researcher at theJulius von Sachs Institute at the University of Wuirzburg.The Hedrich Lab is internationally recognized as a pioneer inmodern ion channel research and for itsexpertise in plant signaling pathways.

For their study, the team investigated the signaling pathways of the model plant Arabidopsis thaliana. "While the defense mechanisms of above-ground plant parts have already been extensively studied, communication within the underground root system remained a mystery for a long time," says Angel Baudon, explaining the background of the project. Understanding root defense against pests like insect larvae or nematodes is of crucial importance for agriculture, as hidden underground damage often leads to massive crop losses.

Alarm Signals Race Through the Plant at Unexpected Speeds

The plant body in general, and the root system in particular, functions as hydrodynamic system. Cells are surrounded by a mechanically stable wall that allows them to build up and maintain a high internal pressure, known as turgor. Cells are hydraulically, metabolically, and electrically interconnected by microscopic junctions called plasmodesmata.

"As soon as a root cell is injured, there is an immediate drop in intracellular pressure, which propagates as a hydraulic wave through the plant's vascular system," explains Baudon. Traveling at a speed of about 75 millimeters per second, this physical communication is many times faster than the propagation of known calcium-electrical waves, which were previously associated with plant defense responses.

This extremely fast, pressure-based injury signaling enables neighboring, healthy regions of the roots to prepare for defense early on. By combining molecular and biophysical approaches, the interdisciplinary team identified two key components within this "injury alarm" system:

The Decoder (MCA1 channels):These mechanosensitive channels translate the physical, mechanical stimuli directly into electrical impulses and calcium signals.

The Amplifier (Glutamate-like receptors):Operating like ion channels, these proteins pick up the original signal and significantly strengthen it.

The Complex Role of Calcium and Electricity in Plant Defense

Wounding a cell or tissue triggers a process that is far more complex than a single, isolated signal. When cellular integrity is destroyed, signaling metabolites such as glutamate and ATP leak out. They diffuse to nearby intact cells, bind to their receptors, and trigger a cascade of secondary calcium-electrical events and likely other signaling mechanisms, as Rainer Hedrich explains.

To decipher the exact role of these signals, the team utilized optogenetics. In this approach, plants were genetically engineered to express light-activated microbial ion channels called channelrhodopsins (CHRs). These channels open exclusively when stimulated by targeted light pulses.

Prof. Shouguang Huangand Prof. Hedrich at SUAT developed specialized CHRs that are permeable to either calcium ions (Ca²⁺) or chloride ions (Cl⁻).By stimulating these modified roots with light pulses, they could selectively provoke either combined calcium-electrical signals or purely electrical signals.

Equipped with these optogenetic tools, Angel Baudon discovered that plants exposed to repeated calcium- but not voltage signals showed a much weaker electrical response after this "Ca²⁺priming." Remarkably, this reduced response was observed not only in the wounded root but also in neighboring roots. This suggests that calcium signaling plays a major role in coordinating how plants adaptively respond to repeated or nearby damage, Baudon speculates.

New Momentum for Sustainable Agriculture

According to the scientists, this newly gained knowledge about mechanical signal processing offers promising strategic approaches for agricultural research. "A deeper understanding of how crops perceive mechanical damage and activate an early-warning system allows for a more targeted optimization of natural plant resistance to root-feeding insects," Hedrich summarizes. The identification of MCA1 as the primary decoder of the pressure drop closes a major gap in the puzzle. In the long term, these insights could help reduce agricultural dependence on chemical pesticides.

Link:https://doi.org/10.1126/sciadv.aef2202