Silica nanoparticles and structural leaf coloration

Advances in photonics and nanostructures have stimulated research on structural coloration in organisms, particularly in animals. The latter research has suggested the possibility of biological structures being templates for the production of new optical devices, through ‘biomimetics and bioinspiration’. Plants are less well studied than animals for structural coloration, or iridescence; perhaps the greater biochemical repertoire of plants reduces the diversity of structures in producing colours. Virtually all blue and green coloration in animals is structural, whereas in flowers and fruits of plants blues are commonly produced by modified anthocyanins.

Plants with iridescent blue leaves are occasionally found in the understoreys of tropical rainforests, and the structural basis for this colour has been found in cellulose layering, either helicoidal or in dense electron-opaque bands, or in the thickness of thylakoid membranes in modified plastids. A recent paper in Annals of Botany shows that the basis for this colour is the combination of helicoid cellulose deposition and the layering of silica nanoparticles in the adaxial epidermal cell wall. Such cells produce a brilliant blue which, combined with the normal chlorophyllous leaf tissue, produces a blue–green leaf.