Always on the bright side: the climbing mechanism of Galium aparine |
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Authors: | Bauer Georg Klein Marie-Christin Gorb Stanislav N Speck Thomas Voigt Dagmar Gallenmüller Friederike |
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Affiliation: | 1.Plant Biomechanics Group, Botanic Garden, Faculty of Biology, University of Freiburg, Schänzlestraße 1, 79104 Freiburg, Germany;2.Evolutionary Biomaterials Group, Department of Thin Films and Biological Systems, Max Planck Institute for Metals Research, Heisenbergstraße 3, 70569 Stuttgart, Germany;3.Functional Morphology and Biomechanics, Zoological Institute, Christian Albrechts University of Kiel, Am Botanischen Garten 1-9, 24108 Kiel, Germany |
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Abstract: | Galium aparine is a herbaceous climbing plant that attaches to host plants mainly via its leaves, which are covered by hooked trichomes. Although such hooks are found on both leaf surfaces, the leaves of G. aparine are mainly positioned upon the leaves of supporting plants and rarely beneath. In order to understand the mechanism underlying this observation, we have studied structural and mechanical properties of single leaf hooks, frictional properties of leaf surfaces, turgor pressure in different leaf tissues and bending properties of the leaves in different directions. Abaxial and adaxial leaf hooks differ significantly in orientation, distribution, structure and mechanical properties. In accordance with these differences, friction properties of leaves depend on the direction of the applied force and differ significantly between both leaf surfaces. This results in a ratchet mechanism. Abaxial leaf hooks provide strong attachment upon the leaves of adjacent plants, whereas adaxial hooks cause a gliding-off from the underside of the leaves of host plants. Thus, the leaves of G. aparine can function as attachment organs, and simultaneously orient themselves advantageously for their photosynthetic function. Further adaptations in turgor pressure or concerning an anisotropy of the flexural stiffness of the leaves have not been found. |
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Keywords: | semi-self-supporter leaf hooks attachment mechanical properties ratchet mechanism |
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