Image Source: Felice Frankel

From: Keyan Qun WeChat Public Account (科研圈)

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 track 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 in their leaves, sending distress signals that stimulate leaf cells to produce compounds to help repair damage or fend off insects and other enemies. The new sensors can use these hydrogen peroxide signals to differentiate between types of stress and different plant species.

“Plants have very intricate and complex forms of internal communication, and we are observing this 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 experience,” said Michael Strano, a professor of chemical engineering at MIT.

These sensors can be used to study how plants respond to different types of stress and are expected to assist agricultural scientists in developing new strategies to enhance crop yields. The researchers demonstrated their method on eight different plants, including spinach, strawberry plants, and arugula, and they believe the device could be used in many more applications.

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 explored the potential of engineering “nano-bionic plants,” incorporating nanomaterials with plants to give them new functions, such as emitting light or detecting moisture shortages. In this new research, he set out to add sensors that could 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 is commonly used in plant molecular research, and studies have shown that plants may use hydrogen peroxide as a signaling molecule, but its precise role is not yet clear.

Lew used a method called lipid exchange membrane permeation (LEEP) to embed the sensors into plant leaves. LEEP is a technique developed by Strano’s lab a few years ago to design nanoparticles that can permeate plant cell membranes. While Lew was deeply involved in figuring out how to embed carbon nanotube sensors, he made an accidental discovery.

He said, “I had been training myself to get familiar with this technology, and during the training, 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 transmit electrical pulse signals in our brains. As the plant released hydrogen peroxide, it triggered the release of calcium in neighboring cells, stimulating those cells to release more hydrogen peroxide.

“It spreads like a domino effect, allowing the wave to travel 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 fend off enemies. These metabolites are often the source of flavors we enjoy in edible plants, and they are produced only when the plant is under stress.

A 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.

Strano said, “In this study, we were able to quickly compare eight different plants, which was not possible with previous tools.”

The researchers tested strawberries, spinach, arugula, lettuce, watercress, and sorrel, finding that different species seem to produce different waveforms, with the concentration changes of hydrogen peroxide over time exhibiting unique patterns. 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 exciting is that the waveform encodes the type of stress the given plant is experiencing,” Strano said. “You can observe the real-time response of plants experiencing almost any new environment.”

Stress Response

The near-infrared fluorescence produced 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 ones found in smartphones. Strano said, “This very inexpensive tool can be used to capture the signals.”

Strano mentioned that the applications of this technology include screening different types of plant varieties and determining 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 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 line of work he is conducting together with colleagues in the interdisciplinary research group for Disruptive and Sustainable Technology for Agricultural Precision (SMART) at MIT-Singapore.

One issue 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 instead of investing energy in crop production. This can reduce overall crop yields, so agricultural researchers are keen to engineer plants to avoid triggering such a response mechanism.

Strano said, “Our sensors allow us to interpret stress signals, accurately understanding the conditions and mechanisms that lead to shade avoidance responses in plants.”

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