Fig. 1.

Plants are pre-stressed structures and, in turn, plant cells respond to mechanical cues. a Pre-stressed structures are more resilient to mechanical fluctuations and are also energy efficient: a suspension bridge, in which beams are under compression and threads under tension, provides a response to the weak ability of concrete to resist compression, while better allowing swinging and dilatation than an arched bridge. A balloon, with an envelope under tension and a gas under compression, is a pre-stressed structure. When exhibiting a cylindrical shape, such an inflated balloon would display an anisotropic stress pattern, with tension being twice as high in the circumferential direction as in the axial direction. b The epidermis of plant aerial organs is under tension, while inner tissues are under compression. Therefore, in the cylindrical stem, tensile stress is predicted to be twice higher transversely than axially. At the apex of the stem, the hemispherical shape of shoot meristem prescribes isotropic tensile stress patterns. Local mechanical conflicts thus arise from cell shape or local differences in growth between adjacent cells. c At the shoot apical meristem, as cells are advected away from the meristem center, cells become exposed to varying degrees and direction of mechanical stresses; in turn, such cues can affect cell division plane orientation, gene expression (for example, STM expression in green) or cell polarity (for example, PIN1 recruitment to the plasma membrane in red)