Abstract
Plant cell morphogenesis depends critically on two processes: the deposition of new wall material at the cell surface and the mechanical deformation of this material by the stresses resulting from the cell's turgor pressure. We developed a model of plant cell morphogenesis that is a first attempt at integrating these two processes. The model is based on the theories of thin shells and anisotropic viscoplasticity. It includes three sets of equations that give the connection between wall stresses, wall strains and cell geometry. We present an algorithm to solve these equations numerically. Application of this simulation approach to the morphogenesis of tip-growing cells illustrates how the viscoplastic properties of the cell wall affect the shape of the cell at steady state. The same simulation approach was also used to reproduce morphogenetic transients such as the initiation of tip growth and other non-steady changes in cell shape. Finally, we show that the mechanical anisotropy built into the model is required to account for observed patterns of wall expansion in plant cells.
Highlights
Plant cells acquire specific shapes according to two major modes of morphogenesis called diffuse growth and tip growth
Wall expansion requires two complementary processes: i) the addition of new wall material by secretion and synthesis at the cell membrane and ii) the mechanical deformation of the wall via the tensional stresses excerted by the internal turgor pressure of the cell
Based on these observations we propose a model where secretion and wall synthesis lead to growth in thickness while mechanical deformation by turgor pressure leads to expansion of the cell surface (Fig. 1A)
Summary
Plant cells acquire specific shapes according to two major modes of morphogenesis called diffuse growth and tip growth. Wall expansion requires two complementary processes: i) the addition of new wall material by secretion and synthesis at the cell membrane and ii) the mechanical deformation of the wall via the tensional stresses excerted by the internal turgor pressure of the cell The integration of these two processes into a single model of cell morphogenesis is a daunting task some observations suggest a possible starting point. In a wide range of cell types it is possible to stop cell enlargement while wall deposition is maintained for some time leading to local thickening of the cell wall (Kiermayer, 1964; Schröter and Sievers, 1971; Roy et al., 1999) This treatment shows that deposition of wall material alone is not sufficient to drive expansion of the cell surface. Based on these observations we propose a model where secretion and wall synthesis lead to growth in thickness while mechanical deformation by turgor pressure leads to expansion of the cell surface (Fig. 1A)
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