Viburnum tinus Fruits Use Lipids to Produce Metallic Blue Structural Color.

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Middleton, Rox 
Sinnott-Armstrong, Miranda 
Ogawa, Yu 

Viburnum tinus is an evergreen shrub that is native to the Mediterranean region but cultivated widely in Europe and around the world. It produces ripe metallic blue fruits throughout winter [1]. Despite its limited fleshy pulp [2], its high lipid content [3] makes it a valuable resource to the small birds [4] that act as its seed-dispersers [5]. Here, we find that the metallic blue appearance of the fruits is produced by globular lipid inclusions arranged in a disordered multilayer structure. This structure is embedded in the cell walls of the epicarp and underlaid with a dark layer of anthocyanin pigments. The presence of such large, organized lipid aggregates in plant cell walls represents a new mechanism for structural coloration and may serve as an honest signal of nutritional content.

TEM tomography, biophotonics, cell walls, fruit color, honest signaling, plant color, plant lipids, plant-animal interaction, seed dispersal, structural color, Anthocyanins, Color, Fruit, Lipid Metabolism, Lipids, Pigmentation, Seed Dispersal, Structure-Activity Relationship, Viburnum
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Curr Biol
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Elsevier BV
Biotechnology and Biological Sciences Research Council (BB/K014617/1)
European Research Council (639088)
Gatsby Charitable Foundation (GAT3395/GLG)
European Commission (301472)
Engineering and Physical Sciences Research Council (EP/G037221/1)
This work was supported by the EPSRC NanoDTC EP/G037221/1 (R.M.) and EPSRC EP/R513179/1 (R.M.), BBSRC David Phillips fellowship [BB/K014617/1] (S.V.), ERC SeSaME ERC-2014-STG H2020 639088 (S.V., Y.O., G.J.), a microMORPH Cross-Training Grant (M.S.A.), a Yale Institute for Biospheric Studies grant (M.S.A.), National Science Foundation (NSF)SF GRFP DGE‐1122492 (M.S.A.), and NSF DBI 1907293 (M.S.A.). We would like to acknowledge the assistance of the Boulder Electron Microscopy Service in preparation and imaging the serial block-face, and the support of the Cambridge Advanced Imaging Centre and the NanoBio-ICMG platform (FR 2607) electron microscopy facility. We are grateful to Heather Whitney and Innes Cuthill for loan of equipment and to two anonymous referees for advice and comments which improved the manuscript.