Plants have the ability to regulate the chemistry of their petals to create iridescent signals.
Some flowers make three-dimensional patterns on their petals, which is a visual cue to pollinators. The iridescent optical effect that is visible to bees is not always visible to humans.
Understanding how plants make petals that please animals could be important for directing future research and policies in agriculture.
There is more to patterning than the eye can see. The formation of ridges on the surface of the young growing petals was thought to be caused by mechanical buckling of the thin, protective cuticle layer on the surface.
The ridges act as gratings that reflect different wavelengths of light, creating a blue-halo effect that bumblebees can see. It wasn't understood why the striations only form in certain flowers.
Edwige Moyroud, who started this research in Professor Glover's lab and is now leading her own research group, has developed the Australian native hibiscus, Venice mallow, as a new model species to understand how and when these occur.
When we tested the model in Venice, we found out that their formation is also very high.
We want to find out how different chemistries can change the mechanical properties of the cuticle. It's possible that different chemical compositions result in a cuticle with differing architecture or with different stiffness and therefore different ways of reacting to the forces experienced by cells as the petals grow.
Plants are able to shape their surfaces due to a combination of processes. Plants are formidable chemists and these results show how they can tune the chemistry of their cuticle to produce different types of flowers. A range of functions can be fulfilled by patterns formed at the tiny scale.
They are striking examples of evolutionary diversification and we are starting to understand how plants can make them.
Current Biology will publish the results.
The Cambridge University Botanic Garden, where the researchers first noticed the iridescent flowers of Venice mallow, is a good example of how these insights can be used.
There are species that grow in different regions that have very different petals. Understanding why petal pattering varies and how this might affect the relationship between the plants and their pollinators can help inform policies in the future.
What drives 3D petals?
The researchers took a more methodical approach to their work. When they observed the development of the petals, they noticed that the cuticle patterns appeared when the cells became larger. They couldn't accurately predict the patterns observed because they couldn't measure physical parameters related to growth. They tried to identify what was missing by taking a step back.
The chemical nature of the material is likely to affect its properties. The researchers looked at the chemistry of the skin and found that it was a controlling factor. A new method from the chemistry field was used to analyze the composition of the cuticle. This shows that the chemistry of the surface of the petals is different.
The striated cuticle has higher levels of dihydroxy-palmitic acid and waxes than the smooth one. They used genes similar to those that control the production of cuticle molecule in a different model plant to change the chemistry of the plants in a way that could be tested if cuticle chemistry was important.
Modification of the texture of the skin can be done without changing the growth of the cells. The 3D folding of the cuticle can be controlled by chemistry. The researchers think that the mechanical properties of the cuticle can be affected by a change in cuticle chemistry.
Edwige Moyroud et al, Cuticle chemistry drives the development of gratings on the petals of a flower. The article was published in the journalcub.
Journal information: Current Biology
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