title: Mechanically, the Shoot Apical Meristem of Arabidopsis Behaves like a Shell Inflated by a Pressure of About 1 MPa.
abstract: In plants, the shoot apical meristem contains the stem cells and is responsible for the generation of all aerial organs. Mechanistically, organogenesis is associated with an auxin-dependent local softening of the epidermis. This has been proposed to be sufficient to trigger outgrowth, because the epidermis is thought to be under tension and stiffer than internal tissues in all the aerial part of the plant. However, this has not been directly demonstrated in the shoot apical meristem. Here we tested this hypothesis in Arabidopsis using indentation methods and modeling. We considered two possible scenarios: either the epidermis does not have unique properties and the meristem behaves as a homogeneous linearly-elastic tissue, or the epidermis is under tension and the meristem exhibits the response of a shell under pressure. Large indentation depths measurements with a large tip (~size of the meristem) were consistent with a shell-like behavior. This also allowed us to deduce a value of turgor pressure, estimated at 0.82±0.16 MPa. Indentation with atomic force microscopy provided local measurements of pressure in the epidermis, further confirming the range of values obtained from large deformations. Altogether, our data demonstrate that the Arabidopsis shoot apical meristem behaves like a shell under a MPa range pressure and support a key role for the epidermis in shaping the shoot apex.
authors.affiliation: Laboratoire Reproduction et Développement des Plantes, INRA, Centre National de la Recherche Scientifique, ENS de Lyon, UCB Lyon 1, Université de Lyon Lyon, France ; Laboratoire Joliot-Curie, Centre National de la Recherche Scientifique, ENS de Lyon, Université de Lyon Lyon, France.
authors.forename: Léna
authors.initials: L
authors.lastname: Beauzamy
authors.affiliation: Laboratoire Reproduction et Développement des Plantes, INRA, Centre National de la Recherche Scientifique, ENS de Lyon, UCB Lyon 1, Université de Lyon Lyon, France ; Laboratoire Joliot-Curie, Centre National de la Recherche Scientifique, ENS de Lyon, Université de Lyon Lyon, France.
authors.forename: Marion
authors.initials: M
authors.lastname: Louveaux
authors.affiliation: Laboratoire Reproduction et Développement des Plantes, INRA, Centre National de la Recherche Scientifique, ENS de Lyon, UCB Lyon 1, Université de Lyon Lyon, France ; Laboratoire Joliot-Curie, Centre National de la Recherche Scientifique, ENS de Lyon, Université de Lyon Lyon, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Hamant
authors.affiliation: Laboratoire Reproduction et Développement des Plantes, INRA, Centre National de la Recherche Scientifique, ENS de Lyon, UCB Lyon 1, Université de Lyon Lyon, France ; Laboratoire Joliot-Curie, Centre National de la Recherche Scientifique, ENS de Lyon, Université de Lyon Lyon, France ; Institut Universitaire de France Paris, France.
authors.forename: Arezki
authors.initials: A
authors.lastname: Boudaoud
keywords: atomic force microscopy; epidermis; indentation; mechanical modeling; shoot apical meristem; turgor pressure