title: Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn.
abstract: The sessile nature of plants demands the development of seed-dispersal mechanisms to establish new growing loci. Dispersal strategies of many species involve drying of the dispersal unit, which induces directed contraction and movement based on changing environmental humidity. The majority of researched hygroscopic dispersal mechanisms are based on a bilayered structure. Here, we investigate the motility of the stork's bill (Erodium) seeds that relies on the tightening and loosening of a helical awn to propel itself across the surface into a safe germination place. We show that this movement is based on a specialized single layer consisting of a mechanically uniform tissue. A cell wall structure with cellulose microfibrils arranged in an unusually tilted helix causes each cell to spiral. These cells generate a macroscopic coil by spiralling collectively. A simple model made from a thread embedded in an isotropic foam matrix shows that this cellulose arrangement is indeed sufficient to induce the spiralling of the cells.
authors.affiliation: The Robert H. Smith Institute of Plant Sciences and Genetics in Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel.
authors.forename: Yael
authors.initials: Y
authors.lastname: Abraham
authors.forename: Carmen
authors.initials: C
authors.lastname: Tamburu
authors.forename: Eugenia
authors.initials: E
authors.lastname: Klein
authors.forename: John W C
authors.initials: JW
authors.lastname: Dunlop
authors.forename: Peter
authors.initials: P
authors.lastname: Fratzl
authors.forename: Uri
authors.initials: U
authors.lastname: Raviv
authors.forename: Rivka
authors.initials: R
authors.lastname: Elbaum
mesh_terms: D001696:Biomechanical Phenomena; D002482:Cellulose / Q000737:chemistry / Q000378:metabolism / Q000648:ultrastructure; D031314:Geraniaceae / Q000033:anatomy & histology* / Q000502:physiology* / Q000648:ultrastructure; D006813:Humidity; D020894:Microfibrils / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D008954:Models, Biological; D053838:Scattering, Small Angle; D058614:Seed Dispersal / Q000502:physiology*; D012639:Seeds / Q000033:anatomy & histology / Q000502:physiology; D014961:X-Ray Diffraction
chemical_list: D002482:Cellulose