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

Date:
August 6, 2020
Source:
Cell Press
Summary:
Instead of relying solely on pigments, the metallic blue fruits
of Viburnum tinus use structural color to reflect blue light,
a mechanism rarely seen in plants. Researchers show that the
fruits use lipid nanostructures 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.



FULL STORY ========================================================================== 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, 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."

========================================================================== Story Source: Materials provided by Cell_Press. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Rox Middleton, Miranda Sinnott-Armstrong, Yu Ogawa, Gianni Jacucci,
Edwige Moyroud, Paula J. Rudall, Chrissie Prychid, Maria Conejero,
Beverley J. Glover, Michael J. Donoghue, Silvia Vignolini. Viburnum
tinus Fruits Use Lipids to Produce Metallic Blue Structural
Color. Current Biology, 2020; DOI: 10.1016/j.cub.2020.07.005 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200806111854.htm

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