Carbon nanotubes embedded in leaves can detect chemical signals produced when plants are damaged.
Image credit: Felice Frankel
Source: MIT News Office
Written by Anne Trafton
Translated by Akin
Reviewed by Qi Yiyin
Engineers at the Massachusetts Institute of Technology (MIT) have developed a method to closely monitor how plants respond to stressors such as injury, infection, and light damage using sensors made from carbon nanotubes. These devices are embedded in plant leaves and report based on hydrogen peroxide signal waves.
Plants communicate internally using hydrogen peroxide, sending distress signals that stimulate leaf cells to produce compounds that help repair damage or deter insect predators. The new sensors can utilize these hydrogen peroxide signals to differentiate between various types of stress and different plant species.
“Plants have a very fine and complex form of internal communication that we are observing for the first time. This means we can see in real-time how living plants respond and how they communicate the specific types of stress they are experiencing,” said Michael Strano, a professor of chemical engineering at MIT.
This sensor can be used to study how plants respond to different types of stress, potentially assisting agricultural scientists in developing new strategies to enhance crop yields. The researchers demonstrated their method on eight different plant species, including spinach, strawberry plants, and arugula, and they believe the device can be applied in many more contexts.
Strano is a senior author of the study, which was published in the journal Nature Plants. MIT graduate student Tedrick Thomas Salim Lew is the lead author of the paper.
Embedded Sensors
For the past few years, Strano’s lab has been exploring the potential of engineering “nano-bionic plants,” which combine nanomaterials with plants to give them new functions, such as luminescence or moisture detection. In this new research, he focused on adding sensors that can report on plant health.
Strano previously developed carbon nanotube sensors that can detect different molecules, such as hydrogen peroxide. About three years ago, Lew began working on embedding these devices into plant leaves. Arabidopsis thaliana, commonly used in plant molecular research, has shown that plants may use hydrogen peroxide as a signaling molecule, but its exact role is still unclear.
Lew used a method called lipid exchange membrane permeation (LEEP) to embed the sensors into plant leaves. LEEP is a technique developed in Strano’s lab a few years ago to design nanoparticles that can penetrate plant cell membranes. While Lew was working on embedding the carbon nanotube sensors, he made an accidental discovery.
“I had been training myself to become familiar with this technology, and during the training, I accidentally injured a plant. Then I saw the evolution of the hydrogen peroxide signal,” he said.
He observed that after the plant was injured, hydrogen peroxide was released from the wound site, creating a wave that spread along the leaf, similar to how neurons transmit electrical pulse signals in our brains. As the plant released hydrogen peroxide, it triggered the release of calcium in adjacent cells, stimulating those cells to release more hydrogen peroxide.
“It’s like a domino effect, allowing the wave to propagate much farther than a single release of hydrogen peroxide,” Strano said. “Once the cells receive the signal wave, they generate more signal waves for further propagation.”
This surge of hydrogen peroxide stimulates plant cells to produce molecules known as secondary metabolites, such as flavonoids or carotenoids, which help the plant repair damage. Some plants also secrete other secondary metabolites to deter predators. These metabolites are often the source of flavors we enjoy in edible plants and are produced only under stress.
The key advantage of this new sensing technology is its applicability to many different plant species. Traditionally, plant biologists conduct extensive molecular biology studies in certain genetically tractable plants, including Arabidopsis and tobacco. MIT’s new method has the potential to be applied to any plant.
“In this study, we were able to quickly compare eight different plants, which was not possible with previous tools,” Strano said.
The researchers tested strawberries, spinach, arugula, lettuce, watercress, and sorrel, finding that different species seem to produce different waveforms, with unique patterns of hydrogen peroxide concentration changes over time. They hypothesize that each plant’s response is related to its ability to cope with damage. Each species appears to respond differently to various stressors, including mechanical damage, infection, heat damage, and light damage.
“For each species, this waveform contains a lot of information, and even more excitingly, the waveform encodes the type of stress experienced by that particular plant,” Strano said. “You can observe the real-time responses of plants experiencing almost any new environment.”
Stress Response
The near-infrared fluorescence generated by the sensors can be imaged using a small infrared camera connected to a Raspberry Pi, a $35, credit card-sized computer similar to the one found in smartphones. Strano said, “This very inexpensive tool can be used to capture signals.”
Strano noted that the applications of this technology include screening different types of plant species to determine their resistance to mechanical damage, light damage, heat damage, and other types of stress. It can also be used to study how different species respond to pathogens, such as the bacteria that cause citrus greening and the fungi that cause coffee rust.
“One thing I’m interested in is understanding why certain types of plants are immune to these pathogens while others are not,” he continued.
Strano is also interested in studying how plants respond to different growing environments in urban farms, a project he is working on with colleagues in the MIT-Singapore Alliance for Research and Technology (SMART) interdisciplinary research group focused on disruptive and sustainable technology for agricultural precision.
One problem they hope to address is the shade avoidance response, a common reaction of plants growing in high-density environments. Such plants will initiate a stress response: reallocating resources to grow taller rather than investing energy in crop production. This can reduce overall crop yields, so agricultural researchers are keen to engineer plants to avoid triggering such response mechanisms.
Strano said, “Our sensors allow us to interpret stress signals and accurately understand the conditions and mechanisms that lead to shade avoidance in plants.”
The research was funded by the Singapore National Research Foundation, the Agency for Science, Technology and Research (A*STAR), and the U.S. Department of Energy Computational Science Graduate Fellowship program.
Original link: http://news.mit.edu/2020/cnt-nanosensor-smartphone-plant-stress-0415
Paper Information
【Paper Title】Real-time detection of wound-induced H2O2 signalling waves in plants with optical nanosensors
【Paper Authors】Tedrick Thomas Salim Lew, Volodymyr B. Koman, Kevin S. Silmore, Jun Sung Seo, Pavlo Gordiichuk, Seon-Yeong Kwak, Minkyung Park, Mervin Chun-Yi Ang, Duc Thinh Khong, Michael A. Lee, Mary B. Chan-Park, Nam-Hai Chua & Michael S. Strano
【Published Journal】Nature Plants
【Publication Date】2020.04.15
【Paper Link】https://www.nature.com/articles/s41477-020-0632-4
【Paper ID】10.1038/s41477-020-0632-4
【Paper Abstract】Decoding wound signalling in plants is critical for understanding various aspects of plant sciences, from pest resistance to secondary metabolite and phytohormone biosynthesis. The plant defence responses are known to primarily involve NADPH-oxidase-mediated H2O2 and Ca2+ signalling pathways, which propagate across long distances through the plant vasculature and tissues. Using non-destructive optical nanosensors, we find that the H2O2 concentration profile post-wounding follows a logistic waveform for six plant species: lettuce (Lactuca sativa), arugula (Eruca sativa), spinach (Spinacia oleracea), strawberry blite (Blitum capitatum), sorrel (Rumex acetosa) and Arabidopsis thaliana, ranked in order of wave speed from 0.44 to 3.10 cm min−1. The H2O2 wave tracks the concomitant surface potential wave measured electrochemically. We show that the plant RbohD glutamate-receptor-like channels (GLR3.3 and GLR3.6) are all critical to the propagation of the wound-induced H2O2 wave. Our findings highlight the utility of a new type of nanosensor probe that is species-independent and capable of real-time, spatial and temporal biochemical measurements in plants.
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