Metallic blue fruits use fat to produce colour and signal a treat for birds

sc604 — Thu, 06 Aug 2020 15:00:00 +0000

̽��ֱ��plant, Viburnum tinus, is an evergreen shrub widespread across the UK and the rest of Europe, which produces metallic blue fruits that are rich in fat. ̽��ֱ��combination of bright blue colour and high nutritional content make these fruits an irresistible treat for birds, likely increasing the spread of their seeds and contributing to the plant’s success.

̽��ֱ��researchers, led by the ̽��ֱ�� of Cambridge, used electron microscopy to study the structure of these blue fruits. While there are other types of structural colour in nature – such as in peacock feathers and butterfly wings – this is the first time that such a structure has been found to incorporate fats, or lipids. ̽��ֱ��results are reported in the journal Current Biology.

“Viburnum tinus plants can be found in gardens and along the streets all over the UK and throughout much of Europe — most of us have seen them, even if we don’t realise how unusual the colour of the fruits is,” said co-first author Rox Middleton, who completed the research as part of her PhD at Cambridge’s Department of Chemistry.

Most colours in nature are due to pigments. However, some of the brightest and most colourful materials in nature – such as peacock feathers, butterfly wings and opals – get their colour not from pigments, but from their internal structure alone, a phenomenon known as structural colour. Depending on how these structures are arranged and how ordered they are, they can reflect certain colours, creating colour by the interaction between light and matter.

“I first noticed these bright blue fruits when I was visiting family in Florence,” said Dr Silvia Vignolini from Cambridge’s Department of Chemistry, who led the research. “I thought the colour was really interesting, but it was unclear what was causing it.”

“ ̽��ֱ��metallic sheen of the Viburnum fruits is highly unusual, so we used electron microscopy to study the structure of the cell wall,” said co-first author Miranda Sinnott-Armstrong from Yale ̽��ֱ��. “We found a structure unlike anything we’d ever seen before: layer after layer of small lipid droplets.”

̽��ֱ��lipid structures are incorporated into the cell wall of the outer skin, or epicarp, of the fruits. In addition, a layer of dark red anthocyanin pigments lies underneath the complex structure, and any light that is not reflected by the lipid structure is absorbed by the dark red pigment beneath. This prevents any backscattering of light, making the fruits appear even more blue.

̽��ֱ��researchers also used computer simulations to show that this type of structure can produce exactly the type of blue colour seen in the fruit of Viburnum. Structural colour is common in certain animals, especially birds, beetles, and butterflies, but only a handful of plant species have been found to have structurally coloured fruits.

While most fruits have low fat content, some – such as avocadoes, coconuts and olives – do contain lipids, providing an important, energy-dense food source for animals. This is not a direct benefit to the plant, but it can increase seed dispersal by attracting birds.

̽��ֱ��colour of the Viburnum tinus fruits may also serve as a signal of its nutritional content: a bird could look at a fruit and know whether it is rich in fat or in carbohydrates based on whether or not it is blue. In other words, the blue colour may serve as an ‘honest signal’ because the lipids produce both the signal (the colour) and the reward (the nutrition).

“Honest signals are rare in fruits as far as we know,” said Sinnott-Armstrong. “If the structural colour of Viburnum tinus fruits are in fact honest signals, it would be a really neat example where colour and nutrition come at least in part from the same source: lipids embedded in the cell wall. We’ve never seen anything like that before, and it will be interesting to see whether other structurally coloured fruits have similar nanostructures and similar nutritional content.”

One potential application for structural colour is that it removes the need for unusual or damaging chemical pigments – colour can instead be formed out of any material. “It’s exciting to see that principle in action – in this case the plant uses a potentially nutritious lipid to make a beautiful blue shimmer. It might inspire engineers to make double-use colours of our own,” said Middleton, who is now based at the ̽��ֱ�� of Bristol.

̽��ֱ��research was supported in part by the European Research Council, the EPSRC, the BBSRC and the NSF.

Reference:
Rox Middleton et al. ‘Viburnum tinus Fruits Use Lipid to produce Metallic Blue Structural Colour.’ Current Biology (2020). DOI: 10.1016/j.cub.2020.07.005

Researchers have found that a common plant owes the dazzling blue colour of its fruit to fat in its cellular structure, the first time this type of colour production has been observed in nature.

I first noticed these bright blue fruits when I was visiting family in Florence. I thought the colour was really interesting, but it was unclear what was causing it

Silvia Vignolini

What gives this metallic blue fruit its colour?

Rox Middleton

Viburnum tinus fruits

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Nanomaterials Up Close: Salt baskets

lw355 — Thu, 05 Jun 2014 14:31:25 +0000

"These baskets are just ordinary salt, dried from droplets of salt water. As the perfectly spherical water droplets dry out, the salt crystallises quickly from the outside, each crystal straining against the rest of the structure and breaking up the spheres.

This image was taken on a scanning electron microscope, enabling us to look far beyond the ordinary micron sized world. In it you can see sort of spherical cages made of cuboid blocks. ̽��ֱ��incompatibility of the crystalline cuboids with the sphere are ripping the cages apart, there's no chance of making this cubic structure form good true spheres.

To me this is an expression of the power of the nanoscale where we are confronted with the limits of our capacity to change materials. We can come up with new ways to manipulate and weave unnatural baskets, but it's the scale at which we find out the true nature of the atoms that form the materials which form us and the rest of our world."

This image was taken while Rox Middleton was doing a summer placement with Dr Alex Finnemore in the Thin Films & Interfaces group in the Cavendish Laboratory, ̽��ֱ�� of Cambridge, using a scanning electron microscope in the ̽��ֱ��'s Nanoscience Centre. Rox is currently a student on the Nanoscience and Technology Doctoral Training Centre (NanoDTC) PhD programme.

'Nanomaterials Up Close' is a special series linked to our 'Under the Microscope' collection of videos produced by Cambridge ̽��ֱ�� that show glimpses of the natural and man-made world in stunning close-up.

This electron microscope picture, reminiscent of man-made baskets or children’s blocks, shows cubic salt crystals that have been forced to form in spheres, as Rox Middleton explains.

To me this is an expression of the power of the nanoscale

Rox Middleton

Nanomaterials Up Close: Salt baskets

Rox Middleton

Salt baskets

̽��ֱ��text in this work is licensed under a Creative Commons Licence. If you use this content on your site please link back to this page. For image rights, please see the credits associated with each individual image.

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̽��ֱ�� of Cambridge - Rox Middleton

Metallic blue fruits use fat to produce colour and signal a treat for birds

What gives this metallic blue fruit its colour?

Nanomaterials Up Close: Salt baskets

Nanomaterials Up Close: Salt baskets