Engineered Glow

Researchers are making huge strides towards creating functional, light-emitting plants. But the jury is out on whether these plants will offer environmental benefits or cause unexpected harms.

WHEN MY GRANDFATHER was young, he caught fireflies and smeared their abdomens on the window pane. Their bioluminescent guts made the window glow. Years later I would catch fireflies in my grandfather’s backyard and gaze at them through a jar. I wouldn’t let him squish them. But we watched them with a common interest, fascinated by the light twinkling from their bodies. There’s something magical and universally captivating about the ability to produce light. We illustrate angels with a soft glow. We travel north to catch a glimpse of Aurora Borealis. Generation after generation we continue to chase fireflies.

Part of that captivation probably stems from the fact that only a limited number of living things emit light. Many deep-sea fish have evolved to be nightlights in the dark. In some warm parts of the world, the bioluminescent plankton Noctiluca scintillans are so concentrated that entire swaths of ocean glow. There’s the three-inch firefly squid that illuminates Japanese tides, and there’s foxfire, light emitted by some fungi that grow on dying wood. Also on the list are Antarctic krill, land snails, and jellyfish.

Yet, for all this diversity, there are no known plants that emit light — or at least, there haven’t been until recently.

THE MASSACHUSETTS INSTITUTE OF TECHNOLOGY (MIT) Department of Chemical Engineering is located in a triangular-shaped building, one of four structures on campus designed by world-renowned architect I.M. Pei. On a sunny March morning, I take the elevator to the fifth floor and enter the department confidently, hoping to give off the look of an engineering student. Yellow doors line the left side of the hallway, accompanied by threatening signs that read “CAUTION: Eye Protection Required” and “Danger Invisible Laser Radiation.” On the other side of the hall is ordinary office space — a compelling dual-brain analogy in the form of interior design.

I’m here to meet with professor and chemical engineer Michael Strano. As I enter his office, Strano mistakes me for a prospective graduate student. He’s wearing a light pink, button-down shirt and sports a salt-and-pepper beard. On the wall, a projector displays a web page opened to his email account. I watch the emails accumulate as we chat about one of his current projects: making plants glow.

A range of terrestrial animals emit light, including New Zealand’s cave-dwelling glowworms that emit a green-blue bioluminescence during the larval and imago stages. Photo by 2il org / Flickr.

As well as certain jelly fish, a variety of deep sea creatures, and Arctic krill. Photo via PickPik.

Generation after generation we continue to chase fireflies, captivated by their ability to produce light. Photo by Fred Huang.

In December 2017, the Strano Research Group at MIT published a paper in the journal Nano Letters about how it modified four plant species — spinach, arugula, kale, and watercress — to emit light. The prototype glowed for 3.5 hours with a yellowish-green light about one-thousandth the amount needed for reading, though one of the project’s trademark photos shows a three-week-old watercress plant faintly illuminating the pages of Paradise Lost. Strano says the next generation of plants will glow more brightly and for substantially longer than a few hours. He hopes someday plants might glow brightly enough to illuminate a room and diminish the need for other types of indoor lighting.

The light-emitting plant project is a part of a broader, relatively new niche of research within nanotechnology that Strano calls “plant nanobionics.” Nano refers to science at a nanoscale (specifically, between 1 and 100 nanometers, a nanometer measuring one billionth of a meter), and bionics refers to functions typically performed by electronic devices. Plant nanobionics is a developing field and thus still quite small; indeed, most of its researchers are Strano’s former students. Strano is currently working on multiple plant nanobionics initiatives, from plants that can detect explosives to those that can communicate with cell phones.

STRANO’S LIGHT-EMITTING PLANT is among the latest iterations of a scientific endeavor that began in the 1980s when a team at the University of California, San Diego modified a tobacco plant to give off light. In November 1986, The New York Times published an article with the headline: “TOBACCO PLANT WITH FIREFLY GENE IMPLANT GROWS,” which explained that, due to a genetic modification, the tobacco plant now emitted visible light in total darkness. Why didn’t the editors take the easy bait: “TOBACCO PLANT WITH FIREFLY GENE IMPLANT GLOWS”? By the article’s last paragraph, it’s clear the alternate headline wouldn’t have exactly followed the Times’ commitment to truth, given that this “glow” could only be seen with the unaided eye “when the scientists stood in the dark for about 10 minutes so that their eyes became acclimatized.”

That effort, however, marked the first time a light-producing gene was successfully transferred into a complex multicellular organism. The team modified the firefly gene for the luciferase enzyme and spliced it into genetic material called plasmids, which were transferred into tobacco plant cells. Once the plants began to grow, they were irrigated with water containing another firefly compound: luciferin, the chemical fuel for light production. Both luciferase and luciferin were needed to illuminate the plant. (Every living thing on Earth that naturally glows uses luciferin. Most, but not all, use luciferase.)

In the past decade, biotechnology startups have continued experimenting with luciferase in plants. In 2010, molecular biologist Alexander Krichevsky at State University of New York, Stony Brook engineered tobacco plant DNA with both luciferase and luciferin to create a glowing plant that he dubbed the “Starlight Avatar.” The plant eventually became “as luminous as a glow-in-the-dark stick-on star,” and Krichevsky started “Bioglow,” a company that auctioned its initial round of prototypes in 2015 for $300 each. But Bioglow struggled to increase the brightness of the plants, and the link to the company’s website now redirects to the unrelated “Dehydrate2Store.”

Strano’s light-emitting plant is among the latest iterations of a scientific endeavor that began in the 1980s.

In 2013, San Francisco-based entrepreneur Antony Evans launched a Kickstarter campaign to make his own light-emitting plant. Like those before him, Evans proposed genetically engineering plants with luciferase and luciferin to make them glow. His company, TAXA Biotechnologies, promised backers a hodgepodge of prizes: a t-shirt with a $25 donation, a “how to make a glowing plant” coffee table book at $90, and, if you invested $10,000, the “grand-daddy of prizes,” a personalized message expressed in DNA.

The “Glowing Plant project” appealed to the public; it pulled in nearly $500,000 from around the world, easily surpassing its $65,000 fundraising goal. The project description claimed this money would go towards “the first step in creating sustainable natural lighting.”

A couple of years passed, and still no plant. Inserting six genes into a plant proved more challenging than Evans expected. After years of hanging on, TAXA Biotechnologies finally announced its defeat. “It was a poor choice of product,” Evans told the MIT Technology Review in summer 2016, shortly before the end. “I personally feel terrible we haven’t shipped yet. But it’s not like we took the money and ran.”

In 2017 — the same year as TAXA’s failure — Strano’s group published a paper on their “Nanobionic Light-Emitting Plant.” But if you Google “glowing plant,” the majority of hits are related to the TAXA Kickstarter project’s demise. A press release on Strano’s work lingers in the middle of the page.

“It was just bad timing,” Strano sighs. “Even though our approach is completely different, I think the public is like, ‘Yeah, right. We’ve heard this before, and it failed.’”

IN THE SPRING OF 2007, six years before Evans launched his Kickstarter, botanist Jodie Holt walked onto a movie set to look at sketches of made-up plants. The crew, producer, and director awaited her input on the zany drawings.

Holt didn’t hide her horror very well. They were too blue.

photo of avatar
The unique attributes of invented plants in the film Avatar are based on real plant characteristics that have been magnified for effect, such as response to touch. The only exception is bioluminescence. Photo via Alamy.

Though many years have passed since that day, Holt recounts this moment to me with some agitation in her voice. “Blue plants on Earth would not survive,” she says. They wouldn’t be able to photosynthesize, since chlorophyll — an essential pigment for photosynthesis — gives plants their green hue.

Holt was hired by Lightstorm Entertainment in March 2007 as a plant consultant for James Cameron’s new movie project, the 2009 blockbuster-to-be Avatar. She was asked to teach Sigourney Weaver how to embody a true botanist, as well as advise on the imaginary plants that would exist on the invented moon of Pandora. Though the flora was to be fictional, Cameron wanted to ensure it was not fantastical.

The next time Holt arrived on set, all the plants were green.

If real plants on Earth can respond to touch, communicate, and shoot poison, why aren’t there any glowing plants?

A few months after the movie premiered, Holt was asked to put together a guide to Pandora’s plants that described the science behind them. Hesitant to invent new science, she told Cameron that, without knowing anything about the environment on Pandora, it would be challenging to scientifically defend these plants. Cameron didn’t miss a beat. He spent two hours describing Pandora’s every detail: light level, atmospheric gases, chemical concentrations in the soil, gravitational strength.

In the end, Holt could defend nearly every one of Pandora’s invented plants based on a real plant characteristic that was magnified for effect, such as response to touch. The only exception was bioluminescence, which doesn’t exist in plants on Earth, but which Holt imagined could have feasibly developed on a planet with such low light levels as Pandora.

If real plants on Earth can respond to touch, communicate, and shoot poison, why aren’t there any glowing plants? I ask Holt.

“I’m surprised they don’t exist,” Holt says. She reasons that the trait probably hasn’t cropped up because of energy distribution. Growth, self-defense, and reproduction are priorities — but glowing? Not nearly as important. In the extreme low-light conditions of Pandora, a bioluminescent plant might attract nocturnal pollinators or frighten a predator. There are other ways to achieve these objectives on Earth, however, which may explain why plants haven’t acquired this particular trait.

TO MAKE A GLOWING plant in the age after Avatar is to fulfill a prediction. By grounding something that sounds imaginary in science, Cameron and Holt created an endpoint; now the science has to catch up and meet it.

Strano’s team appears to have done just that: Their plants already glow brightly enough to be used as indirect lighting, and the method is straightforward and reliable — and fast, because it works on mature plants. (To genetically modify a tree to glow, scientists would have to change the DNA in the seed and then wait years for it to grow.)

The chemical reaction itself is fairly simple: In the presence of ATP, or adenosine triphosphate, (the fuel of the cell), magnesium, and oxygen, luciferin undergoes oxidation, losing a few electrons and emitting light as a byproduct; the luciferase enzyme accelerates the whole process. To get the reaction’s components into the plant, Strano’s team inserts them into three different types of biocompatible nanoparticles made of silica, polyethylene glycol, and chitosan. The nanoparticles act as little boxes that hold, respectively, luciferase, luciferin, and another enzyme that lengthens the duration of the light emission.

‘Whether it will lead to further development I don’t know, but the fact that it works — and works well — is remarkable.’

Once the reaction ingredients are packaged into nanoparticles, scientists transfer the particles into the leaves. They do this by giving the plants a bath — more specifically, a fully submerged, highly pressurized bath, during which they blast nanoparticles in solution through the tiny pores in the leaves.

Harvard professor and chemist George Whitesides, well-known for his work in nanotechnology, believes Strano’s team has accomplished an impressive feat. “The fact that they can get a large collection of non-plant materials with different activities to work together with the plant’s metabolism, without having some component fail, and without quickly killing the plant, is really astonishing,” he wrote to me in an email. “Whether it will lead to further development I don’t know, but the fact that it works — and works well — is remarkable.”

The important next step will be to optimize for light intensity and duration. Not surprisingly, this requires a trade-off. In short bursts, the glowing plant can be very bright; for sustained light, it is dimmer. The team has found that they can affect these two factors drastically by adjusting the amount and size of nanoparticles. With time, they predict that they can achieve a light duration of 17 days at low but meaningful brightness, or alternatively a duration of one day at a level perfect for reading a book. Because the reactants eventually run out, plant owners would need to reapply them to the leaves. Strano believes people will eventually be able to accomplish this with a spray, overcoming the current need for a pressurized bath.

Other researchers have taken a different, fungi-focused approach. Working with mushrooms, they were able to identify the structure of the protein that allows certain fungi to glow. In the process, they discovered a new type of luciferin that is chemically distinct from previously identified luciferins, including that used by Strano. This “new” luciferin is produced by caffeic acid, which occurs naturally in plants and is compatible with plant biochemistry. Researchers have since injected genes from a bioluminescent mushroom into a tobacco plant to achieve a glow, a process they say is more cost-effective long-term than using nanoparticles. (Seon-Yeong Kwak, lead author of the MIT study, says that the materials needed to synthesize the nanoparticles are not expensive. She acknowledges that the luminescent reagents are expensive, but says the cost could decrease with mass production.)

Photo by
Some fungi, like Bitter Oyster (Panellus Stipticus), that grow on dying wood emit a bioluminescence known as foxfire. Researchers have injected mushroom genes into a tobacco plant to achieve a glow. Photo by Ylem.

But the continuous glow that comes with these types of genetically-modified plants would prohibit their ability to be switched off when it’s time to sleep. A nanobionic plant lamp, on the other hand, shuts down naturally when it runs out of reactants. Someday Strano hopes to create a mechanism, perhaps in the form of another spray, that could act like a light switch. His team found that adding the naturally-occurring chemical dehydroluciferin inhibits the reaction, stopping the plant from emitting light, while a small dose of chitosan restarts the reaction.

WHY PLANTS? I asked Strano. For one thing, he began, they’re generally low cost. They’re also easily recyclable: Just toss them in a compost pile. We have a lot to learn from plants, considering they pump water efficiently, make their own energy, store energy, self-repair — the list goes on. They’re doubly carbon negative too, which means not only do they not release carbon into the atmosphere, but they’re also made of carbon, thus keeping that carbon from contributing to atmospheric levels.

Another obvious appeal is, of course, the potential environmental benefits associated with replacing at least some electrical demand with plant-based lights. In addition to household lighting, Strano can imagine a world where streetlights are replaced with glowing trees.

Moving a glowing plant from the containment of a research facility to outdoor environments raises a host of concerns.

Strano believes the energy benefits of such an application could be enormous. The US Energy Information Administration estimates that, in 2018 alone, the commercial sector, which includes buildings and street lighting, consumed about 141 billion kilowatt-hours, or 16 billion watts of power. A significant amount of this energy gets lost along the way: The total percentage of overall losses in the US electrical grid is approximately 6 percent, and the global average is closer to 30 percent. Because the light-emitting plant would be off the grid, no energy would be lost in the production of light. Given that the going rate per kilowatt-hour ranges from 8 to 33 cents in the US, it could be a huge money saver if glowing plants replaced even a portion of traditional lighting.

But moving a glowing plant from the containment of a research facility to outdoor environments raises a host of concerns. For example, how would a glowing tree affect the ecosystem? How might light emission confuse animal behavior?

“My first impression is that the impacts of a glowing tree may be minimal, because, remember, you’re replacing a street lamp, which is a lot brighter and already has impacts on wildlife,” Strano says. Another concern would be the impact on animals eating the glowing plants. The materials within the plants themselves are technically edible; in fact, all three nanoparticles are used as food additives. “For lighting something outside, we want something that’s completely safe,” Strano explains. But while initial toxicity risk may be low, more research needs to be done on how these particles could accumulate along the food chain. Strano concedes that “a lot has to happen before we bring technology outside.”

I discussed the potential pros and cons of the endeavor with Holt, who studied plant ecosystems in college. “It’s such a complicated question,” she says. “In a time in our history where we’re more concerned about climate change and negative environmental impacts than ever, I think the benefits of substituting a live tree for an energy-consuming streetlight would outweigh the risks.”

But, she adds, it depends on the currency you’re using. If you’re measuring the impact on energy consumption, the glowing plant is a good option. But perhaps it has a negative impact on wildlife behavior. How do you compare the two? “You have to first define what your goals are,” Holt says. “What are your criteria for success? How do you define benefit and risk?”

A MAJOR SOURCE of anxiety around modifying living things is the risk of spread. There’s a long history of humans introducing species to new regions where they wreak havoc on native organisms. For instance, the Japanese honeysuckle, introduced to the United States in 1806, has overrun the East Coast and smothered native species in the process. This is a plant that already existed in nature; how would it affect our ecosystems to introduce a plant species that we modified? What happens if someone plants a glowing seedling in their backyard, and it reproduces? Could it spread across the country, contributing to light pollution and pushing out critical plant species?

Methods that involve changing nature tend to inspire deep unease in people, and for good reason.

Methods that involve changing nature tend to inspire deep unease in people, and for good reason. The smallest miscalculation could domino, causing monumental damage in ways that no one anticipated. “To have a system that could escape and be heritable would be a really bad thing,” Holt says.

That’s why the key selling point of Strano’s nanotechnology technique — besides its efficacy — is that it doesn’t change the plant’s genome in any way. Instead, Strano’s team infuses materials into the plant. Because no genes are changed, the plant’s acquired superpowers aren’t hereditary.

But nanotechnology is a relatively new field, still in the early days of research. Because of that, some environmental groups, including Friends of the Earth, advocate a precautionary approach to the field, pointing to mounting evidence of health and environmental impacts associated with nanoparticles, and the ongoing uncertainty surrounding their use.

In the US, investigation into the biological and ecological impacts of this technology has been spearheaded by the two national Centers for Environmental Implications of Nanotechnology (CEINT) established in 2008, one at Duke University and one at the University of California, Los Angeles. “When we started this research, we were, globally, taking a more contaminant view of nanomaterials,” says Dr. Christine Hendren, executive director of CEINT at Duke University. “But we haven’t seen the type of acute, toxic response that people were worried about at the beginning.”

CEINT’s research has shown that the impact of nanomaterials primarily depends on environment and context. For instance, the nanosilica used in Strano’s light-emitting plant is extremely dangerous to the respiratory system while in the air, but it can’t damage lungs when inside of a plant. Similarly, toxicity of nanoparticles depends not only on if the particle is toxic at its regular size, but also what other materials it’s exposed to in the environment.

Hendren believes that the biggest implication of nanotechnology will be a positive one, especially in applications involving renewable energy. But, she says, nanomaterials should be regarded carefully on a case-by-case basis, and scientists should engage with other stakeholders and disciplines to understand potential implications. “We need to consider what are the ways that these things could get out of the matrix they’re in while inside the plant, and what happens if they do,” says Hendren.

Strano agrees on the need to proceed with caution: “We are not rushing out into a field and transforming plants.”

While health and environmental impacts should be taken into consideration alongside laboratory development, it’s possible they may end up being moot points unless glowing plants could someday become mainstream. Paul Hawken, editor of Project Drawdown, which analyzed hundreds of possible environmental solutions to create a prioritized agenda for tackling climate change, doubts that will happen. “These kinds of breakthroughs pour out of research universities,” he said in an email. “They are fascinating science, but there is no validation of their commercial viability. There is usually a 20-year lag time before they become commercial, and only 1 percent ever reach that point.” In other words, glowing plants probably aren’t making his list of the best ways to address the climate crisis. The amount of system overhaul necessary to expand plant lighting would be massive and expensive.

Regardless, TAXA’s failure demonstrated that the science should be solid before anyone even teases the idea of commercial viability. Indeed, some of the biggest doubters are Strano’s own colleagues, who are unsure his efforts can technically succeed. “Can a plant be a lamp? Can it talk to your cell phone? Can it measure chemicals in the environment?” Strano asks. He thinks the answer to all these questions is yes, but acknowledges that the rest of science isn’t there yet. “These techniques are new and weird, and they’re not typically used in plants.”

But he believes the project can teach scientists about these groundbreaking nanotechnology techniques, which will, he hopes, lead to several useful applications. In 2017, shortly after Strano’s team released a paper on sentinel plants — plants that are used to monitor environmental stimuli — the US Defense Advanced Research Projects Agency (DARPA) started the Advanced Plant Technologies program, which “seeks to develop plants capable of serving as next-generation, persistent, ground-based sensor technologies to protect deployed troops.” (While it refers here to using plants only as potential sensors, DARPA’s research around modifying living organisms for use in biological warfare is quite controversial.)

Strano sees this as a small victory for the future of plant nanobionics. “I think people are understanding,” he says. “This is how the field will evolve. I’m willing to be patient.”

STRANO REALIZES THAT any transition that moves glowing plants into homes will depend not only on the science, but also — importantly — on normalizing the concept. “We have an uphill burden in convincing people that this can be a real thing,” he says. How do you do that with something that currently exists only in Avatar?

Strano’s idea: Put it in an actual house. Or at least, a miniature house inside of a museum. This past January marked the end of a 33-week installation, part of the “Nature — Cooper Hewitt Design Triennial” exhibition, in New York’s Smithsonian Museum of Design. Instead of scaling up the watercress plant to room-size, they scaled down a New York City tenement building to match the current science.

The building model offered peepholes for visitors to look inside at rooms where glowing plants illuminated dining room tables and reading nooks occupied by tiny figurines.

“It’s part of this outreach to get people familiar and comfortable with the idea that your light could come from a plant,” Strano explains. “The person at the exhibit gets a sense of what it’d be like to live in a house illuminated by plants.”

Still, some people find foreign the concept of owning even non-glowing plants. Much like a pet, plants require maintenance. “Are people going to water plants when they can turn on a light switch? It’s an interesting question,” says Whitesides. In the same way a person might prefer cats or dogs, some people like plants while others are indifferent to them. The latter population would be a harder sell when it comes to popularizing plant lights. But as to the plants already occupying people’s homes, Whitesides muses, “Why shouldn’t they emit light at the same time?”

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