title: Structural features of reconstituted wheat wax films.
abstract: Cuticular waxes are essential for the well-being of all plants, from controlling the transport of water and nutrients across the plant surface to protecting them against external environmental attacks. Despite their significance, our current understanding regarding the structure and function of the wax film is limited. In this work, we have formed representative reconstituted wax film models of controlled thicknesses that facilitated an ex vivo study of plant cuticular wax film properties by neutron reflection (NR). Triticum aestivum L. (wheat) waxes were extracted from two different wheat straw samples, using two distinct extraction methods. Waxes extracted from harvested field-grown wheat straw using supercritical CO2 are compared with waxes extracted from laboratory-grown wheat straw via wax dissolution by chloroform rinsing. Wax films were produced by spin-coating the two extracts onto silicon substrates. Atomic force microscopy and cryo-scanning electron microscopy imaging revealed that the two reconstituted wax film models are ultrathin and porous with characteristic nanoscale extrusions on the outer surface, mimicking the structure of epicuticular waxes found upon adaxial wheat leaf surfaces. On the basis of solid-liquid and solid-air NR and ellipsometric measurements, these wax films could be modelled into two representative layers, with the diffuse underlying layer fitted with thicknesses ranging from approximately 65 to 70 Å, whereas the surface extrusion region reached heights exceeding 200 Å. Moisture-controlled NR measurements indicated that water penetrated extensively into the wax films measured under saturated humidity and under water, causing them to hydrate and swell significantly. These studies have thus provided a useful structural basis that underlies the function of the epicuticular waxes in controlling the water transport of crops.
authors.affiliation: Biological Physics Group, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Elias
authors.initials: E
authors.lastname: Pambou
authors.affiliation: Biological Physics Group, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK.
authors.forename: Zongyi
authors.initials: Z
authors.lastname: Li
authors.affiliation: STFC ISIS Facility, Rutherford Appleton Laboratory, Didcot OX11 0QX, UK.
authors.forename: Mario
authors.initials: M
authors.lastname: Campana
authors.affiliation: STFC ISIS Facility, Rutherford Appleton Laboratory, Didcot OX11 0QX, UK.
authors.forename: Arwel
authors.initials: A
authors.lastname: Hughes
authors.affiliation: STFC ISIS Facility, Rutherford Appleton Laboratory, Didcot OX11 0QX, UK.
authors.forename: Luke
authors.initials: L
authors.lastname: Clifton
authors.affiliation: Institut Laue-Langevin, 71 avenue des Martyrs, 38000 Grenoble, France.
authors.forename: Philipp
authors.initials: P
authors.lastname: Gutfreund
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
authors.forename: Jill
authors.initials: J
authors.lastname: Foundling
authors.affiliation: Syngenta, Jealott's Hill International Research Centre, Bracknell, Berkshire RG42 6EY, UK.
authors.forename: Gordon
authors.identifier: 0000-0002-2742-8838
authors.initials: G
authors.lastname: Bell
authors.affiliation: Biological Physics Group, School of Physics and Astronomy, University of Manchester, Oxford Road, Manchester M13 9PL, UK j.lu@manchester.ac.uk.
authors.forename: Jian R
authors.identifier: 0000-0001-5648-3564
authors.initials: JR
authors.lastname: Lu
mesh_terms: D008567:Membranes, Artificial; D016062:Porosity; D014908:Triticum / Q000737:chemistry*; D014885:Waxes / Q000737:chemistry*
chemical_list: D008567:Membranes, Artificial; D014885:Waxes
keywords: Triticum; cuticular films; neutron reflection; plant waxes; wheat