What if plants glowed in the dark?

On a summer night, fireflies twinkle. In some forests, mushrooms glow green.

What if trees and flowers glowed too? Would the night be bright?

Some living things can make their own light. It's called bioluminescence (by-oh-loo-mih-NESS-ens). Fireflies flash in summer fields, some mushrooms glow green on the forest floor, and in the deep ocean most animals at some depths make light.

The plants in your garden don't glow. But what if they did? In this thought experiment, you will find out how glowing living things make light and why, meet the plants scientists have made glow, and imagine what a glowing world might be like.

Bioluminescence is light produced by an organism through a chemical reaction. In fireflies, an enzyme called luciferase combines with a molecule called luciferin, using oxygen and the energy molecule ATP. Glowing fungi use genes and chemistry of their own, which is why scientists could later borrow mushroom genes for plants.

This thought experiment imagines plants that glow. It looks at the organisms that already do, at why they glow, and at real attempts to engineer glowing plants, separating what has been measured from what is imagined.

Fireflies glow to find each other. They flash their lights on and off.

In the deep sea, lots of animals glow. Some mushrooms glow too.

There are more than 2,000 kinds of fireflies. Their flashing lights are messages: each kind has its own flash pattern, and the females answer from the ground. Even young firefly larvae glow.

In the ocean, glowing is common. NOAA scientists report that 80 percent of the animals living between 200 and 1,000 meters deep make their own light, including many fish, squid and jellies. On land, a few kinds of mushrooms glow too: by 2015, scientists had found 71 glowing kinds among about 100,000 known kinds of fungi.

Fireflies make light when luciferase combines with luciferin in the presence of magnesium ions, ATP and oxygen; the light carries very little heat. Adult flashes are species-specific courtship signals, and all firefly larvae are bioluminescent (University of Illinois Extension). There are over 2,000 firefly species.

NOAA Ocean Exploration reports that 80 percent of animals living between 200 and 1,000 m in the open ocean are bioluminescent, most commonly fish, squid and gelatinous zooplankton. Among fungi, 71 of roughly 100,000 described species were known to glow in 2015 (NPR).

Imagine flowers and trees that glow softly at night.

The light would be dim, like a night-light. It might help people see a path.

Imagine waking up at night to a garden of softly glowing trees and flowers. It would be beautiful. But how bright would it be?

The glowing plants scientists have made so far are dim. In 2017, MIT engineers made watercress glow for about three and a half hours, but its light was only about one-thousandth of what you need to read by. A glowing world might look magical, yet a dim glow might also affect night animals such as fireflies, which need darkness to see each other's signals.

Engineered glow is still faint. MIT's nanobionic watercress (Kwak, Strano and colleagues, Nano Letters, 2017) glowed for about 3.5 hours at roughly one-thousandth of reading-light intensity. The researchers' long-term hope is plants as unplugged desk lamps or even streetlights.

A world of glowing plants might change the night environment. Fireflies, for example, rely on dark skies: University of Illinois Extension notes that brighter night skies make it harder for them to find mates. Whether faint plant light would matter to them is unknown, so this remains an idea, not a prediction.

Fireflies glow to say hello to other fireflies.

Some mushrooms glow to call insects. The insects carry their spores to new places.

Scientists think glowing often helps living things survive. Fireflies flash to find mates. In the deep sea, light can help animals find food, find each other or defend themselves, though scientists still aren't sure of every reason.

In Brazil, a mushroom that glows green at the base of young palm trees was put to the test. Scientists made fake mushrooms, gave some a green light and covered them all in sticky glue. More flies, ants and beetles stuck to the glowing ones. The light seems to attract insects that spread the mushroom's spores through the still forest air.

Bioluminescence may help organisms find food, reproduce and defend themselves, though NOAA notes that its main purpose is often not well understood. For fireflies, flashes are courtship signals.

For the Brazilian mushroom Neonothopanus gardneri, Jay Dunlap (Dartmouth) and Cassius Stevani's lab (University of São Paulo) tested an idea with acrylic replicas, some lit with green LEDs and all coated in glue: flies, ants and beetles were caught in greater numbers on the lit ones. The team's interpretation is that the glow lures insects that disperse spores in dense forest with little wind.

Scientists have made a petunia flower that glows!

It uses ideas borrowed from a glowing mushroom. Its newest buds glow the brightest.

About 40 years ago, a research team put a firefly gene into a tobacco plant. It glowed, but only weakly, and only when it was given an extra chemical. Later, in 2017, MIT engineers made watercress glow by filling its leaves with tiny particles carrying the firefly's light chemicals, without changing its genes.

Then scientists borrowed genes from glowing fungi. The result, the Firefly Petunia, was approved by the US Department of Agriculture in fall 2023 and went on sale in 2024. Its glow keeps itself going without any added chemical, and its newest buds glow brightest.

Early engineered plants carried the firefly luciferase gene but could not sustain light without an added substrate; as Keith Wood put it, 'you've got glow, but it was a weak glow.' MIT's 2017 approach used nanoparticles, not genetic modification, to deliver luciferase, luciferin and coenzyme A.

The Firefly Petunia, developed by a team including Wood at the company Light Bio, carries a set of genes from fungi, mainly from a bioluminescent mushroom, that form a self-sustaining light cycle; it has no firefly genes. It took about a decade to develop, was approved by the USDA in fall 2023 and went on sale online in February 2024. Its petals give a greenish-white glow, brightest in new buds; no measured brightness was reported.