Plant mecano-perception and long-distance signaling: role of hydraulic signals

It is now well accepted that plants can detect mechanical stimuli such as wind or touch and respond to these stimuli by modifying their development and growth – a process called thigmo-morphogenesis (Jaffe et al 2002, Braam 2004, Telewski 2006). A fascinating feature of this mechanical-induced-growth response is that it is not only local, but also non-local: bending locally a stem or a branch can induce a very rapid (~ min) modification of the growth far away from the stimulated area (Coutand et al 2000, Pruyn et al 2000). The origin and nature of this signal is still not understood and remains a scientific barrier for the understanding of the growth modulation in plants.

Plants gravisensing: a granular flow problem?

Gravity perception by plants plays a key role in their development and adaptation to environmental change (gravitropism), from the moment a shoot grows upward after germination to the control of the final posture (Moulia & Fournier 2009). A crucial step in this gravisensing occurs in specific cells, the statocytes, which contain small grains of starch called the statoliths (Morita 2010). The grains being denser than the surrounding intracellular fluid, they sediment, and give the direction of gravity. When the plant is inclined, a redistribution of auxin transporters (the plant growth hormone) is triggerred and the resulting auxin gradients causes an asymmetric growth and a global bending of the organ.

Fast motion and rapid actuation in plants

Some plants generate fast movements when mechanically stimulated, and use this ability to disperse their seeds, protect themselves against predators or get extra-nutrients (Dumais & Forterre 2012, Poppinga et al 2013). Among these nastic movements, the carnivorous plant Venus flytrap (Dionaea muscipula), whose leaves snaps together in a fraction of second to catch insect, has long been a paradigm for study (Darwin 1875, Escalante-Perez et al. 2011).

Soft matter inspired by plants

Plants sensing and motility mechanisms offer unique strategies to design smart fluids and new soft materials. We first turn our attention to the remarkable flowing properties of the statoliths found in plant gravisensing. Recently, decisive progress has been made in our understanding of the flow of particulate media like granular media and macroscopic suspensions (Forterre & Pouliquen 2008, Boyer et al 2011, deGiuli 2015). Compared to these systems, two ingredients can affect the flowing behavior of micrometer-size particles like statoliths: fluctuation (either thermally activated or due to the surrounding living intracellular liquid) or short-range interaction forces.

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