The most intense colour blue in the plant kingdom?

New research investigates structural colour in fruits and flowers.

11 Dec 2012

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The intensely colored blue fruits of Pollia condensata.

Colour is important to plants for various reasons. In leaves of some plants, bright coloration can signal a warning to herbivorous animals. Brightly coloured flowers can readily attract potential pollinators such as insects, and intense coloration in fruits can attract a bird or animal that could act as a dispersal agent.

Photo: Electron micrograph showing cell wall

Transmission electron micrograph showing cell wall microfibrils of fruit wall of Pollia condensata

Colour that is pigment-based is sometimes enhanced by structural means, to increase gloss or iridescence. For example, the blue colour of the fruits of Pollia condensata (Commelinaceae) is more intense than that of any previously described biological material.

Using transmission electron microscopy at Kew, combined with optical imaging and spectroscopy at Cambridge University, a recent study published in the Proceedings of the National Academy of Sciences of the USA has demonstrated that this intense coloration in Pollia fruits is caused by helicoidally stacked cellulose microfibrils in the cell walls of the fruit wall. This particular type of structural colour has rarely been reported in plants, though it occurs relatively commonly in animals.

Funded by the Leverhulme Trust and with input from international collaborators, a joint research programme is currently investigating the biological and physical bases of several different types of structural colour in plants.

Item from Dr Paula Rudall (Head of Micromorphology, RBG Kew)

Kew Scientist, issue 42

Article Reference:

Vignolini, S., Rudall, P.J., Rowland, A.V., Reed, A., Moyroud, E., Faden, R.B., Baumberg, J.J., Glover, B.J. & Steiner, U. (2012). Pointillist structural color in Pollia fruit. PNAS 109: 15712–15715.