Imagine if a plant in a farmer's field could warn a grower that it needs water? Or if a farmer could signal to plants that dry weather lies ahead, thereby prompting the plants to conserve water?
It may sound extraordinary, but researchers at the Center for Research on Programmable Plant Systems (CROPPS), which is funded by a five-year, $25 million National Science Foundation (NSF) grant, have taken a major step toward advancing such two-way communication with plants.
A new study, published April 23 in the Proceedings of the National Academy of Sciences, has solved a century-old conundrum of how plants internally signal stress. By understanding how plant communication systems work, the team may then begin to exploit those signals to create plants that can communicate with people and each other, and be programmed to respond to specific stressors.
Vesna Bacheva, a postdoctoral associate in CROPPS, tests part of a prototype system designed to detect a stress response in a gene-encoded reporter plant.
The solution lies in the negative pressure that exists within a plant's vasculature, which is required for keeping water inside its stems, roots and leaves when it's dry. Stressors alter the pressure balance inside the plant, which then launches motion in the plant's fluid that can carry mechanical and chemical signals throughout the plant, to counter a stressor and restore balance.
"We are trying to build a foundational knowledge of understanding how communication in plants happens," said first author Vesna Bacheva, a postdoctoral associate in CROPPS and a Schmidt Science Fellow. "Our framework provides a mechanistic understanding of what drives signals from one place to another and explains how mechanical and chemical signals could propagate."
Bacheva works in the labs of co-authors Abe Stroock '95, the Gordon L. Dibble '50 Professor of chemical and biomolecular engineering in Cornell Engineering, and Margaret Frank, associate professor of plant biology in the School of Integrative Plant Science in the College of Agriculture and Life Sciences.
"It's a very important step forward in an area that is surprisingly nascent in terms of true mechanistic understanding," Stroock said.
More than a century ago, scientists began to question how plants might transmit signals from one part of the plant to another to elicit a response to stressors. Scientists hypothesized that perhaps plants used hormones or chemicals to communicate, while others suggested that they used mechanical signals.
Bacheva and colleagues have now developed a predictive model and unified framework that explains how mechanical and chemical signals are transmitted throughout the plants when stressors cause changes in pressure.
The vasculature of plants is made up of a system of tubes that are under pressure and which exert pressure on elastic tissues. When a plant is wounded, such as when a caterpillar bites into a leaf, a pressure change occurs, which can elicit coupled downstream responses.
The researchers suggest that pressure shifts can cause a mass flow of water through the plant that carries chemicals released by cells at the site of the wound to the rest of the plant. One hypothesis is that such chemicals may trigger production of a toxic acid that repels insects. Pressure changes may also trigger mechanosensitive channels located around the vasculature to open and release calcium or other ions that have downstream effects. A calcium flux could then potentially prompt expression of genes that are part of a defensive response.
"We are trying to develop reporter plants that will tell us what they're experiencing at the moment," Bacheva said. These include pigment-based plants that change color, or fluorescent plants that light up when they need water. The ultimate vision is to have bidirectional communication, so not only could a reporter plant communicate that it needs water, a farmer might also inform a plant that it could be dry for many days and the plant should use water more efficiently.
"We're at a point at CROPPS where we are simultaneously investigating the molecular biology, biophysics, engineering design and integration toward agronomic reality with brand-new concepts and technologies," Stroock said.
Co-authors include CROPPS researcher Jesse Woodson, associate professor of plant sciences at the University of Arizona; Fulton Rockwell, a research scientist at Harvard University; and Jean-Baptiste Salmon, a researcher at the University of Bordeaux, France.
The Air Force Office of Scientific Research also provided additional funding.
