Showcasing natural products in the gardens they come from

“One day I was walking to a meeting through the arboretum, and it struck me,” says University of California, Davis, chemistry professor Jared T. Shaw. “Wouldn’t it be cool to have displays on medicinal properties of plants?”

Others have had similar thoughts, the result being not one but two natural products exhibits in the UC Davis Arboretum, one developed by Shaw and the other by a separate group of natural products researchers.

“It’s exactly what we at the arboretum see as our goal,” says Elaine Fingerett, the arboretum’s academic coordinator. Several years ago, the 100-acre arboretum changed its mission. The arboretum formerly had exhibits that merely helped visitors understand the plants that were in the gardens. Now, the arboretum is used in part to inform students and visitors about the work of UC Davis scholars.

Shaw’s exhibit grew from a multiyear collaboration with a local high school science teacher. Shaw visited the class to talk about his work in synthesizing natural products and other biologically active molecules; then the class visited the UC Davis Arboretum to learn more about the natural products in plants. Each student researched a natural product and presented it to the class. The students voted on a favorite, which then went on temporary display in the arboretum.

“If high school kids are helping create the content, they’ll help communicate things in a way that’s interesting to nonscientists,” Shaw says.

Then, using the students’ displays as inspiration, Shaw worked with arboretum staff to develop a permanent installation. The exhibit as envisioned will include five signs that describe selected medicinal plants, their uses, a natural product from them, and other information such as medicinal plant traditions. The budget for the full project is $4,200. Shaw has raised the money for two signs so far, and he hopes to add the rest over the next three years. “Fund-raising takes a lot of time,” he says.

Choosing the final set posed a challenge that Shaw hadn’t anticipated: “There’s a bit of a liability aspect to medicinal plant displays,” he says. Plants used medicinally for one purpose can also be toxic or hallucinogenic. Shaw would’ve liked to include a display for Datura wrightii, which is in the nightshade family and is sometimes called “western Jimson weed.” It produces scopolamine, which is used clinically to treat nausea. But the plant also produces hallucinogenic alkaloids. “It is sacred to Native Americans and also abused by people,” Shaw says.

Of the approved displays, his favorite is one about aspirin, which is derived from salicin made by red willow trees. “It’s one of the first examples of a synthetic drug,” Shaw says. “Willow bark was used in many cultures for centuries, and it’s this chemically modified extract that’s this very useful drug.”

While Shaw was working on his project, another one germinated independently. Chemistry graduate student Quynh Nhu Nguyen met Fingerett at an “Art of Science” event at which Nguyen displayed some of her paintings. “We talked about trees and plants and chemical compounds, and thought it might be interesting if we identified molecules from plants and told people about it,” Nguyen says.

Her adviser, chemistry professor Dean J. Tantillo, was immediately on board. But although he works on biosynthetic mechanisms involving terpene natural products, he’s not a plant expert, so he recruited plant biology professor Philipp Zerbe. “I love terpenes, but I don’t know which terpene is in which plant,” Tantillo says. “Philipp seems to know that without having to look it up.” Zerbe’s research focuses on identifying the biosynthetic pathways for terpenes and engineering them into yeast to make new products.

The team developed a temporary exhibit called “Walking in the Woods with Chemistry,” which highlights 13 natural products and the plants that make them. In choosing the natural products, Zerbe started with compounds from plants that would be generally familiar to people. He narrowed down the list by selecting compounds that are used in pharmaceutical or industrial products and are also the subject of research at UC Davis. The signs give information about the chemical, why the plant makes it, its traditional and modern uses, and related research at UC Davis. Viewers can use smartphones to scan two-dimensional barcodes that direct to the project’s website.

Nguyen’s favorite chemical in the exhibit is ginkgolide B. “I like it because the tree itself is really beautiful, and the compound is quite interesting because it has so many rings,” she says.

Zerbe’s is marrubiin, produced by horehound species. “Horehound has been used for centuries. Ancient Greeks used it for respiratory diseases and it’s still used in cough lozenges,” he says. “Over the last two to three years, there have also been preclinical trials showing that marrubiin has fairly strong antidiabetic efficacy.”

The signs are accompanied by 3-D printed models of each chemical. The Tantillo lab already had the printer, and Nguyen optimized the structures and printed them. The models are made of acrylonitrile butadiene styrene and have generally stood up well to the outdoor environment, although they’ve lost the occasional hydrogen.

An opening event to launch the exhibit attracted roughly 50 people, many of them local nonscientists. “They were so interested in learning more about the plants,” Nguyen says. “They asked so many questions, including about how plants make the molecules.” The team is discussing whether to make the exhibit permanent or to spin it off into something new.

“It’s been a fun project,” Zerbe says. “I thought it was a great avenue for reaching out to the public. The work that we do is a lot of biotechnology, and there’s a lot of controversy about it. It’s nice to be able to talk to people about what we do and the issues they may have with it.”