This fruit attracts birds with an unusual way of making itself metallic blue

August 06, 2020

There's a reason why blue fruits are so rare: the pigment compounds that make fruits blue are relatively uncommon in nature. But the metallic blue fruits of Viburnum tinus, a popular landscaping plant in Europe, get their color a different way. Instead of relying solely on pigments, the fruits use structural color to reflect blue light, something that's rarely seen in plants. Researchers reporting August 6 in the journal Current Biology show that the fruits use nanostructures made of lipids in their cell walls, a previously unknown mechanism of structural color, to get their striking blue--which may also double as a signal to birds that the fruits are full of nutritious fats.

"Structural color is very common in animals, especially birds, beetles, and butterflies, but only a handful of plant species have ever been found to have structural color in their fruits," says co-first author Miranda Sinnott-Armstrong, a postdoctoral researcher at the University of Colorado-Boulder. "This means that V. tinus, in addition to showing a completely novel mechanism of structural color, is also one of the few known structurally colored fruits."

Senior author Silvia Vignolini (@VignoliniLab), a physical chemist at the University of Cambridge, has been interested in the plants for nearly 10 years. "I actually found this Viburnum in a garden in Italy and observed that they looked weird, so we measured them at the time but didn't have conclusive results. It was kind of always on the back of my mind," she says. As her team grew, they become more interested in V. tinus and eventually had the capability to examine the structure of the fruits using electron microscopy. "Before we got the images, we were just seeing all these blobs," she says. "When we found out that those blobs were lipids, we got very excited."

While most plants have cell walls made of cellulose, used to make cotton and paper, V. tinus fruit cells have much thicker walls with thousands of globular lipids arranged in layers that reflect blue light. The structure formed by this so-called lipid multilayer allows the fruits to create their vibrant blue color while containing no blue pigment. "This is very strange because globular lipids like these are not usually found in this arrangement in the cell wall, as they are normally stored inside the cell and used for transport," says co-first author Rox Middleton, a physicist who studied the optical response of the fruits during her PhD and is now a postdoctoral researcher at the University of Bristol. "We also believe that this lipid may contribute to the fruit's nutrition. That means that the fruit can demonstrate how nutritious it is by being a beautiful, shiny blue."

This extra nutrition would be important for V. tinus's main consumers: birds that disperse the plant's seeds. Although the researchers can't say for sure whether the lipids are used as fat by the birds that consume them, there is reason to believe they might be. If so, the researchers suggest that the metallic blue color made by the lipid multilayer could indicate to the birds that if they see this striking blue, the fruit in question will have enough nutrients to make it a worthwhile meal. "While birds have been shown to be attracted to blue fruits," says Vignolini, "other blue fruits that we have studied essentially don't have any nutritional value."

Going forward, the researchers want to see how widespread blue structural color is in fruits to understand its ecological significance. They had never seen this type of lipid multilayer in a biomaterial before, but since their discovery, they've begun to take notice of other species. "We actually realize now that there are some older electron microscopy pictures from other plants where you can see the blobs. The researchers didn't know that they were lipids at the time, or that lipids could even form this type of structure, but our research suggests that they very well could be, meaning this structure may not be limited to Viburnum," Vignolini says.

Additionally, learning how V. tinus can use such a unique mechanism to make color may have implications for how we color our own foods. "There are lots of problems connected to food coloration," says Vignolini. She adds that once this mechanism is better understood, it could potentially be used to create a healthier, more sustainable food colorant.

But right now, Vignolini is just excited her initial hunch paid off: "I've been working on this type of photonic structure for quite a while, and I was beginning to think there were no new ways to make it--at some point you've seen so many that you think, 'This is more or less the end, it's going to be difficult to find something new,'" she says. "Instead, we discovered much more than what we expected."
-end-
This work was supported by the EPSRC NanoDTC, BBSRC David Phillips fellowship, ERC SeSaME, a microMORPH Cross-Training Grant, a Yale Institute for Biospheric Studies grant, and the National Science Foundation.

Current Biology, Middleton et al.: "Viburnum tinus fruits use lipids to produce metallic blue structural colour" https://www.cell.com/current-biology/fulltext/S0960-9822(20)30995-7

Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit: http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.

Cell Press

Related Science Articles from Brightsurf:

75 science societies urge the education department to base Title IX sexual harassment regulations on evidence and science
The American Educational Research Association (AERA) and the American Association for the Advancement of Science (AAAS) today led 75 scientific societies in submitting comments on the US Department of Education's proposed changes to Title IX regulations.

Science/Science Careers' survey ranks top biotech, biopharma, and pharma employers
The Science and Science Careers' 2018 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Science in the palm of your hand: How citizen science transforms passive learners
Citizen science projects can engage even children who previously were not interested in science.

Applied science may yield more translational research publications than basic science
While translational research can happen at any stage of the research process, a recent investigation of behavioral and social science research awards granted by the NIH between 2008 and 2014 revealed that applied science yielded a higher volume of translational research publications than basic science, according to a study published May 9, 2018 in the open-access journal PLOS ONE by Xueying Han from the Science and Technology Policy Institute, USA, and colleagues.

Prominent academics, including Salk's Thomas Albright, call for more science in forensic science
Six scientists who recently served on the National Commission on Forensic Science are calling on the scientific community at large to advocate for increased research and financial support of forensic science as well as the introduction of empirical testing requirements to ensure the validity of outcomes.

World Science Forum 2017 Jordan issues Science for Peace Declaration
On behalf of the coordinating organizations responsible for delivering the World Science Forum Jordan, the concluding Science for Peace Declaration issued at the Dead Sea represents a global call for action to science and society to build a future that promises greater equality, security and opportunity for all, and in which science plays an increasingly prominent role as an enabler of fair and sustainable development.

PETA science group promotes animal-free science at society of toxicology conference
The PETA International Science Consortium Ltd. is presenting two posters on animal-free methods for testing inhalation toxicity at the 56th annual Society of Toxicology (SOT) meeting March 12 to 16, 2017, in Baltimore, Maryland.

Citizen Science in the Digital Age: Rhetoric, Science and Public Engagement
James Wynn's timely investigation highlights scientific studies grounded in publicly gathered data and probes the rhetoric these studies employ.

Science/Science Careers' survey ranks top biotech, pharma, and biopharma employers
The Science and Science Careers' 2016 annual Top Employers Survey polled employees in the biotechnology, biopharmaceutical, pharmaceutical, and related industries to determine the 20 best employers in these industries as well as their driving characteristics.

Three natural science professors win TJ Park Science Fellowship
Professor Jung-Min Kee (Department of Chemistry, UNIST), Professor Kyudong Choi (Department of Mathematical Sciences, UNIST), and Professor Kwanpyo Kim (Department of Physics, UNIST) are the recipients of the Cheong-Am (TJ Park) Science Fellowship of the year 2016.

Read More: Science News and Science Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.