Real-Time Detection of Plant Stress Using Nanosensors

Image Source: 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 embedded in plant leaves, reporting 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 distinguish between different types of stress and various plant species.

“Plants have very fine and complex internal communication forms, and we are now observing them 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 feel,” 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 improve crop yields. Researchers demonstrated their method in eight different plants, including spinach, strawberry plants, and arugula, and they believe the device can be used in more areas.

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” by combining nanomaterials with plants to give them new functionalities, such as luminescence or moisture detection. In this new research, he set out to add 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 trying to embed these devices in plant leaves. Arabidopsis thaliana is commonly used in plant molecular research, which has suggested 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 in plant leaves. LEEP is a technique developed by Strano’s lab a few years ago to design nanoparticles that can permeate plant cell membranes. As Lew was working on embedding carbon nanotube sensors, he made an accidental discovery.

He said, “I had been training myself to be familiar with this technology, and during the training process, I accidentally injured a plant. Then I saw the evolution of the hydrogen peroxide signal.”

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 in our brain transmit electrical pulse signals. As the plant releases hydrogen peroxide, it triggers the release of calcium in adjacent cells, stimulating those cells to release more hydrogen peroxide.

“Like a domino effect, this allows the wave to propagate much further than a single release of hydrogen peroxide,” Strano said. “After receiving the signal wave, cells 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 they are only produced 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 research in certain genetically tractable plants, including Arabidopsis and tobacco. MIT’s new method has the potential to apply to any plant.

Strano said, “In this study, we were able to quickly compare eight plants, which could not be done with previous tools.”

Researchers tested strawberry, spinach, arugula, lettuce, water celery, and sorrel, finding that different species seemed to produce different waveforms, with unique patterns of hydrogen peroxide concentration changes over time. They hypothesize that each species’ response is related to its ability to cope with damage. Each species appears to respond differently to various stressors, including mechanical injury, 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 given plant,” Strano said. “You can observe the real-time responses of plants in 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 inside a smartphone. Strano said, “This very inexpensive tool can 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, working with colleagues in the interdisciplinary research group at the MIT-Singapore Alliance for Research and Technology (SMART) on disruptive and sustainable technology for agricultural precision.

One problem they hope to address is the shade avoidance response of plants, 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 upstream and downstream.”

This 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

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