Viburnum tinus Fruits Use Lipids to Produce Metallic Blue Structural Color.
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 . Despite its limited fleshy pulp , its high lipid content  makes it a valuable resource to the small birds  that act as its seed-dispersers . 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.
European Research Council (639088)
Gatsby Charitable Foundation (GAT3395/GLG)
European Commission (301472)
Engineering and Physical Sciences Research Council (EP/G037221/1)