Dionysia tapetodes, an evergreen alpine shrub with bright yellow flowers in the spring, thrive in harsh highland environments. Its leaves are thin and thick, and they grow close together in a spherical, dome-like shape, unlike your usual houseplant. According to Raymond Wightman, a plant biologist at the University of Cambridge, the species is also fluffy-looking because it performs something unusual: The plant produces a wool-like substance that grows into long strands that wrap across the plant’s leaves “like a spider’s web,” according to Wightman.
A team of experts explored what this “wool” is comprised of and how the plant develops it in a new study co-authored by Wightman and published in the journal BMC Plant Biology.
Plant samples from the Cambridge University Botanic Garden were used in the study, which was collected by a Bristol University professor around 1970 from the species’ natural range, which stretches from Turkmenistan’s border to mountainous parts of Iran and Afghanistan. The researchers flash-froze many leaves and split them open with a cryo-scanning electron microscope, allowing them to see the hair cells that were creating the wool threads.
To assess the chemical makeup of these wool threads, the team utilized a Raman microscope, which fires a laser through a lens, generating a color spectrum that can be studied to discover what chemicals are there. They discovered a compound known as “flavone” as well as two related molecules. The researchers were able to section the leaves even finer using another electron microscope.
“And that was the first time we spotted the holes,” Wightman says.
They were able to identify microscopic gaps in the cell walls roughly the same diameter as the fuzzy fibers using an electron microscope, with a waxy substance outside the cell wall functioning as a seal to keep the contents of the cell from flowing out. The plants looked to be frying the woolly fibers inside the hair cells, which subsequently poked their way out through the cell wall perforations.
Wightman says the holes were surprising because defects in a plant’s cell membrane usually result in disaster: “You put holes in cell walls, and they’ll burst.”
The crew couldn’t watch the hole-punching in operation because electron microscopes can only view a sample that is fixed in time. Future initiatives that could provide a better look at how wool is manufactured are being considered by the researchers. “That’s the first time we’ve seen anything like it in biology,” Wightman says.
Why do the Dionisia tapetodes produce wool? That remains a mystery. “When you consider the limited resources a mountain plant has”—they frequently don’t receive much water and must make do with nutrient-poor soil and more UV exposure, for example—“it’s a lot of effort to be creating this wool,” Wightman adds. Because a related plant that doesn’t generate the wool dries up more rapidly in the summer, the researchers believe it could be acting as a form of sunblock to shield the plants from high-altitude radiation.
“I believe plants are and always will be the best chemists,” Wightman says. “And they’re going to keep surprising us.”