title: Stiffness gradients in vascular bundles of the palm Washingtonia robusta.
abstract: Palms can grow at sites exposed to high winds experiencing large dynamic wind and gust loads. Their stems represent a system of stiff fibrous elements embedded in the soft parenchymatous tissue. The proper design of the interface of the stiffening elements and the parenchyma is crucial for the functioning of the stem. The strategy of the palm to compromise between stiff fibre caps and the soft parenchymatous tissue may serve as a model system for avoiding stress discontinuities in inhomogeneous and anisotropic fibre-reinforced composite materials. We investigated the mechanical, structural and biochemical properties of the fibre caps of the palm Washingtonia robusta at different levels of hierarchy with high spatial resolution. A gradual decrease in stiffness across the fibre cap towards the surrounding parenchymatous tissue was observed. Structural adaptations at the tissue level were found in terms of changes in cell cross sections and cell wall thickness. At the cell wall level, gradients across the fibre cap were found in the degree of orientation of the microfibrils and in the lignin level and composition. The impact of these structural variations in the local material stiffness distribution is discussed.
authors.affiliation: Plant Biomechanics Group, Albert-Ludwigs-Universität Freiburg, 79104 Freiburg, Germany. markus.rueggeberg@mpikg.mpg.de
authors.forename: Markus
authors.initials: M
authors.lastname: Rüggeberg
authors.forename: Thomas
authors.initials: T
authors.lastname: Speck
authors.forename: Oskar
authors.initials: O
authors.lastname: Paris
authors.forename: Catherine
authors.initials: C
authors.lastname: Lapierre
authors.forename: Brigitte
authors.initials: B
authors.lastname: Pollet
authors.forename: Gerald
authors.initials: G
authors.lastname: Koch
authors.forename: Ingo
authors.initials: I
authors.lastname: Burgert
mesh_terms: D028023:Arecaceae / Q000502:physiology*; D003238:Connective Tissue / Q000502:physiology; D008401:Gas Chromatography-Mass Spectrometry; D013056:Spectrophotometry, Ultraviolet; D013718:Tensile Strength; D014961:X-Ray Diffraction