Using structural colour to track length scale of cell‐wall layers in developing Pollia japonica fruits

Summary: Helicoidally arranged layers of cellulose microfibrils in plant cell walls can produce strong and vivid coloration in a wide range of species. Despite its significance, the morphogenesis of cell walls, whether reflective or not, is not fully understood. Here we show that by optically monitoring the reflectance of Pollia japonica fruits during development we can directly map structural changes of the cell wall on a scale of tens of nanometres. Visible‐light reflectance spectra from individual living cells were measured throughout the fruit maturation process and compared with numerical models. Our analysis reveals that periodic spacing of the helicoidal architecture remains unchanged throughout fruit development, suggesting that interactions in the cell‐wall polysaccharides lead to a fixed twisting angle of cellulose helicoids in the cell wall. By contrast with conventional electron microscopy, which requires analysis of different fixed specimens at different stages of development, the noninvasive optical technique we present allowed us to directly monitor live structural changes in biological photonic systems as they develop. This method therefore is applicable to investigations of photonic tissues in other organisms

Self-assembled, disordered structural color from fruit wax bloom

Many visually guided frugivores have eyes highly adapted for blue sensitivity, which makes it perhaps surprising that blue pigmented fruit are not more common. However, some fruits are blue even though they do not contain blue pigments. We investigate dark pigmented fruits with wax blooms, like blueberries, plums, and juniper cones, and find that a structural color mechanism is responsible for their appearance. The chromatic blue-ultraviolet reflectance arises from the interaction of the randomly arranged nonspherical scatterers with light. We reproduce the structural color in the laboratory by recrystallizing wax bloom, allowing it to self-assemble to produce the blue appearance. We demonstrate that blue fruits and structurally colored fruit are not constrained to those with blue subcuticular structure or pigment. Further, convergent optical properties appear across a wide phylogenetic range despite diverse morphologies. Epicuticular waxes are elements of the future bioengineering toolbox as sustainable and biocompatible, self-assembling, self-cleaning, and self-repairing optical biomaterials

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 [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.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

Using structural colour to track length scale of cell‐wall layers in developing Pollia japonica

Summary: Helicoidally arranged layers of cellulose microfibrils in plant cell walls can produce strong and vivid coloration in a wide range of species. Despite its significance, the morphogenesis of cell walls, whether reflective or not, is not fully understood. Here we show that by optically monitoring the reflectance of Pollia japonica fruits during development we can directly map structural changes of the cell wall on a scale of tens of nanometres. Visible‐light reflectance spectra from individual living cells were measured throughout the fruit maturation process and compared with numerical models. Our analysis reveals that periodic spacing of the helicoidal architecture remains unchanged throughout fruit development, suggesting that interactions in the cell‐wall polysaccharides lead to a fixed twisting angle of cellulose helicoids in the cell wall. By contrast with conventional electron microscopy, which requires analysis of different fixed specimens at different stages of development, the noninvasive optical technique we present allowed us to directly monitor live structural changes in biological photonic systems as they develop. This method therefore is applicable to investigations of photonic tissues in other organisms

Beetle Iridescence Avoidance Response Data

Raw data from the "Beetle iridescence induces an avoidance response in naïve avian predators" study. Data also contains a 'read me' file with further instructions

Multiple origins of lipid-based structural colors contribute to a gradient of fruit colors in Viburnum (Adoxaceae).

Structural color is poorly known in plants relative to animals. In fruits, only a handful of cases have been described, including in Viburnum tinus where the blue color results from a disordered multilayered reflector made of lipid droplets. Here, we examine the broader evolutionary context of fruit structural color across the genus Viburnum. We obtained fresh and herbarium fruit material from 30 Viburnum species spanning the phylogeny and used transmission electron microscopy, optical simulations, and ancestral state reconstruction to identify the presence/absence of photonic structures in each species, understand the mechanism producing structural color in newly identified species, relate the development of cell wall structure to reflectance in Viburnum dentatum, and describe the evolution of cell wall architecture across Viburnum. We identify at least two (possibly three) origins of blue fruit color in Viburnum in species which produce large photonic structures made of lipid droplets embedded in the cell wall and which reflect blue light. Examining the full spectrum of mechanisms producing color in pl, including structural color as well as pigments, will yield further insights into the diversity, ecology, and evolution of fruit color