Biomechanics of Plant Cell Growth


Plant cell growth is an irreversible yielding of the cell wall to the internal turgor pressure of the cell. Plant cells can control their expansion by modulating the structure and material properties of their wall. One major level of control is the distribution and orientation of the stiff cellulose microfibrils within the wall. When aligned, the microfibrils impart the wall with mechanical anisotropy which allows cells to expand preferentially along one direction. Moreover, growth is possible only when the stress in the wall exceeds a critical yield stress, also under cellular control. This article summarizes the key models that have been put forward to account for these aspects of cell growth. We begin with the now classic model by James Lockhart which reconciles the mechanical and hydraulic aspects of cell expansion. We then give an overview of newer modelling efforts to account for the complexity of cell wall mechanics.

Key Concepts:

  • Plant cell growth is an irreversible change in cell size involving stretching of the cell wall driven by the internal turgor pressure of the cell.

  • Growth is measured as the relative elemental growth rate (REGR).

  • The two main modes of cell morphogenesis are tip growth and diffuse growth.

  • For a cell to grow the cell surface must expand and water must enter the cell. The Lockhart equation encapsulates the balance between these two processes.

  • Under most circumstances, the rate of cell growth is limited by the extensibility of the cell, wall whereas the resistance to the influx of water is comparatively low (plant cell growth is said to be extensibility limited).

  • Cellulose microfibrils provide the cell wall with anisotropic mechanical properties which allow cells to expand along a preferred direction.

Keywords: cell wall; turgor pressure; Lockhart equation; cell growth; anisotropy; biomechanics

Figure 1.

Mode of morphogenesis in walled cells. (a) Tip growth as observed in pollen tubes and root hairs. (b) Diffuse growth in the Nitella internodal cell. Four successive internodal cells of increasing lengths are shown. (c) Intercalary growth in the Phycomyces sporangiophore. The relative growth rate is shown as shades of green (light green, slow growth and dark green, fast growth).

Figure 2.

Surface extension in a diffusely growing cell. (a) Typical displacement of material points on the surface of a cylindrical cell. Note that the cell elongates, widens and twists as it grows. (b) The deformation of a circumferential strip of wall material. The axial and transverse strain rates, and the shear rate are respectively: ɛ̇A=ln(H/h)/Δt, ɛ̇θ=ln(R/r)/Δt and ɛ̇=tanα/Δt.

Figure 3.

Force equilibrium in a cylindrical cell.

Figure 4.

Framework for the analysis of the cellular morphogenesis. Boxes delimit the three main aspects of cellular morphogenesis.

Figure 5.

Relationship between turgor pressure and cell elongation as observed in Chara and Nitella. (a) Increases or decreases in turgor pressure lead to an abrupt (elastic) change in cell length followed by a gradual transition to a new elongation rate. (b) The elongation rate depends strongly on the cell's pressure and shows a marked yield pressure (approximately 50% of normal pressure) below which growth is not possible (based on data published in Proseus et al., ).



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Jordan, Benjamin M, and Dumais, Jacques(Mar 2010) Biomechanics of Plant Cell Growth. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0022336]