Pointillist structural color in Pollia fruit
- Silvia Vignolinia,
- Paula J. Rudallb,
- Alice V. Rowlandb,
- Alison Reedc,
- Edwige Moyroudc,
- Robert B. Fadend,
- Jeremy J. Baumberga,
- Beverley J. Gloverc,1, and
- Ullrich Steinera,1
- aCavendish Laboratory, Department of Physics, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE, United Kingdom;
- bJodrell Laboratory, Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, United Kingdom;
- cDepartment of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, United Kingdom; and
- dSmithsonian Institution, National Museum of Natural History, Department of Botany, MRC 166, PO Box 37012, Washington, DC 20013-7012
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Edited by David A. Weitz, Harvard University, Cambridge, MA, and approved August 13, 2012 (received for review June 13, 2012)
Abstract
Biological communication by means of structural color has existed for at least 500 million years. Structural color is commonly observed in the animal kingdom, but has been little studied in plants. We present a striking example of multilayer-based strong iridescent coloration in plants, in the fruit of Pollia condensata. The color is caused by Bragg reflection of helicoidally stacked cellulose microfibrils that form multilayers in the cell walls of the epicarp. We demonstrate that animals and plants have convergently evolved multilayer-based photonic structures to generate colors using entirely distinct materials. The bright blue coloration of this fruit is more intense than that of any previously described biological material. Uniquely in nature, the reflected color differs from cell to cell, as the layer thicknesses in the multilayer stack vary, giving the fruit a striking pixelated or pointillist appearance. Because the multilayers form with both helicoidicities, optical characterization reveals that the reflected light from every epidermal cell is polarized circularly either to the left or to the right, a feature that has never previously been observed in a single tissue.
Footnotes
- ↵1To whom correspondence may be addressed. E-mail: bjg26{at}cam.ac.uk or u.steiner{at}phy.cam.ac.uk.
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Author contributions: S.V., B.J.G., and U.S. designed research; S.V., P.J.R., A.V.R., A.R., and E.M. performed research; R.B.F. contributed new reagents/analytic tools; S.V. and J.J.B. analyzed data; and S.V., J.J.B., B.J.G., and U.S. wrote the paper.
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The authors declare no conflict of interest.
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This article is a PNAS Direct Submission.
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This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1210105109/-/DCSupplemental.
