A flower’s nano-powers

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    A flower’s nano-powers

    When it comes to shapes and colours, flowers are one of nature’s most praised objects – but there is more to them than meets the eye. Tobias Wenzel and Silvia Vignolini reveal an ingenious strategy flowers use to become coloured and attract pollinators Iridescent nature: Nature is full of structural colours, not just on animals like peacocks and butterflies, but on plants such as flowers and ferns too. (Courtesy: Edwige Moyroud; Lucas Bustamente/Nature PL; Shutterstock/Jakapan Kammanem; Luiz Claudio Marigo/Nature PL) Have you ever wondered why some butterflies and fruits can shine with a metallic, iridescent blue and beetles can decorate themselves with golden shells – but there is no paint that lets you depict these dynamic colours directly? Well, it all comes down to how those organisms create the colour. Paints and pigments simply absorb part of the visible light spectrum and reflect the rest to create the colour we see – white if they reflect all the visible light, black if no reflection occurs, and other colours when only part of the spectrum is reflected. The special vibrant colours of the butterflies and beetles, in contrast, are obtained thanks to transparent materials that have nanoscale structures. As these features are similar in size to the wavelength of light, they can interact with it to create what are known as “structural colours” ( Rep. Prog. Phys. 71 076401 ). Many birds, insects, reptiles, bacteria and even mammals display an incredible variety of structural colours, which may be dynamic, unique and brighter than standard pigmentation. As Isaac Newton had suspected, the bright colours displayed by a peacock, for example, are structure based and cannot be achieved by paint-like pigmentation. Plants can create structural colours too, even though they have received far less scientific attention than animals. Indeed, structural colour can be found in everything from flowers and ferns to fruit, leaves and even seaweeds. In addition to extending the available range and brightness of colours beyond those created by pigmentation, structural colours can offer further advantages to biological organisms as they can be easily tuned and adapted. Pigments have to be specially synthesized by an organism, requiring advanced chemistry, many genes and a lot of energy. In contrast, many structural colours are formed from more abundant materials, such as cell-wall cellulose or wax. This can be a huge evolutionary benefit, being easier to evolve and to adapt, as well as being “cheaper” to make. Indeed, structural colour can be altered by only changing the size of the structures producing them ( PNAS 109 15712 ). Floral striations Figure 1: The optical effect of diffraction gratings is based on the interference of light from its periodic elements, leading to the wavelength-dependent enhancement of light at some angles, and the cancellation of electromagnetic radiation at others. (Click for more detail) Some flower petals have a particularly interesting example of colour-generating nanostructures. Known as striations, these are parallel surface wrinkles in the petals’ cuticle – the upper wax layer of flowers – and […]