Mechanical buckling of petals produces iridescent patterns

A new study by our researchers in collaboration with researchers in the Sainsbury Laboratory shows flowers are employing a materials science phenomenon typically associated with failures in structural engineering to produce exquisite three-dimensional petal patterns to lure pollinators.

 

In civil engineering “buckling” is a dirty word with the buckling of beams and columns leading to mechanical failure – and is something that engineers want to avoid. But for some plants, buckling is being employed to advantage.

 

Flowers use several different strategies to lure pollinators. Chemical colour from pigments is just one of these strategies and recent research is finding that iridescence could be just as important for attracting pollinators like bees. This optical effect is produced by an intricate pattern of nano-scale ridges on the surface of petals that diffract light to cause iridescence, like that seen on the surface of CDs or soap bubbles, but how the plant develops these ridges was not known.

 

This new study, published in Cell Reports, demonstrates that plants employ buckling to precisely alter the deformation of the surface of petals in hibiscus flowers. “The petal striations on hibiscus flowers develop during petal growth, and Professor Beverley Glover’s team, who were the first to discover the iridescence properties in flowers, suspected that they may be caused by mechanical properties as the petals expanded”, said Dr Sarah Robinson in the University of Cambridge’s Sainsbury Laboratory and lead author on the paper.

 

Working with members of the Department of Plant Sciences' Evolution and Development Research Group headed up by Professor Beverley Glover, Dr Robinson was able to test this model by using a robotic system, called ACME (automated confocal micro-extensometer) that she had earlier developed to measure mechanical properties in plants. They applied a specific force to stretch immature hibiscus (Hibiscus trionum) petals that had not yet developed striations to see if it was possible to mechanically induce the patterns.

 

“The ACME developed by Dr Sarah Robinson gave us the unique chance to investigate if Hibiscus striation patterns could be mechanically induced.’’ said Dr Chiara Airoldi, in the University of Cambridge’s Department of Plant Sciences and first author on the paper.

 

“We saw striations appear almost instantaneously when a mechanical stress was applied. This told us that it was buckling that was causing a wrinkling of the petal surface and not a slower biological process," said Dr Robinson.