Abstract
The bright and intense blue-green coloration of the fruits of Margaritaria nobilis (Phyllanthaceae) was investigated using polarization-resolved spectroscopy and transmission electron microscopy. Optical measurements of freshly collected fruits revealed a strong circularly polarized reflection of the fruit that originates from a cellulose helicoidal cell wall structure in the pericarp cells. Hyperspectral microscopy was used to capture the iridescent effect at the single-cell level.
Highlights
In some plants, the cell walls of selected tissues exhibit helicoidal architecture, in which multiple adjacent wall layers are composed of aligned cellulose fibrils that rotate along a helical screw [1]
Using light microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), fruits were obtained from the Royal Botanic Gardens, Kew, either from alcohol-preserved specimens or dried herbarium specimens from two separate collections, the first collected by Spruce in 1855, and the second collected by Belem and Mendes in 1964
Our results demonstrate that the intense blue-green coloration of the fruits of M. nobilis is a structural effect, resulting from a helicoidal cellulose structure in the multi-layered cell walls of the pericarp
Summary
The cell walls of selected tissues exhibit helicoidal architecture, in which multiple adjacent wall layers are composed of aligned cellulose fibrils that rotate along a helical screw [1] Despite this regular construction, considerable flexibility exists in the dimensions and geometry of the multi-layered structure [2]. Helicoidal cell-wall architecture has been reported in a broad range of land plants, including mosses, ferns, gymnosperms and angiosperms [2,4], but they are common in beetle exoskeletons [5]. Most fruit colour is produced by pigmentation [18], but a few plant species produce highly metallic and intensely coloured fruits by means of a nanostructured multi-layered cell wall, including the commelinid monocot Pollia condensata [11,17] and the rosid eudicot Margaritaria nobilis [19,20]
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