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Series of photographs for the book -The Art of acclimating plants, the garden of the Villa Thuret - by Catherine Ducatillion and Landy Blanc-Chabaud, published by Editions Quae. © INRA, SLAGMULDER Christian

Plants also feel, move and communicate!

Sensitivity and coordinated motricity

Plants have a more complex behaviour than was thought for many years: on the one hand, they are able to perceive their neighbours, and on the other to perceive themselves in space and adapt their movements accordingly.

By Pascale Mollier, translated by Vicky Hawken
Updated on 09/04/2014
Published on 07/30/2014

Plants perceive each other

Charles Darwin was responsible for evidencing the tropism of plants relative to light.  Working with his son Francis in 1880, he demonstrated that grasses will bend towards a lateral light source.  

Plants contain several types of pigments (chlorophyll, carotenoids) that are analogous with our ocular pigments but spread throughout their surface, thus allowing them to detect different parts of the light spectrum (natural light, blue or red light).

"They are also endowed with a highly original capacity that we do not have," explains Bruno Moulia. "They can distinguish dark red from light red.  This is very important because plants reflect dark red light and absorb light red light.  A plant that receives a lot of dark red thus detects the presence of another nearby plant.  It adapts by moving away from it or accelerating its growth upwards in order to retain its share of the light".  In 1999, this scientist showed that a maize plant could detect other plants situated more than 3 metres away.

Plants sense each other in space

  The two keys to stem straightening: sensitivity to gravity and proprioception.. © INRA, Bruno Moulia
The two keys to stem straightening: sensitivity to gravity and proprioception. © INRA, Bruno Moulia

When a young shoot is inclined, it will gradually straighten itself.  The molecular mechanism underlying this movement is known: when the stem is inclined, auxin membrane receptors are redistributed to its lower surface.  Auxin thus accumulates on this lower surface which then grows more rapidly, hence the straightening of the stem.

However, INRA and CNRS research scientists have shown that this mechanism does not suffice to explain how stems return to the vertical.  Indeed, they modelled this straightening on the computer while taking account of this mechanism alone, and showed that the stem did not stabilise and oscillate around the vertical because each element in it was trying to straighten itself separately, thus driving the others.  It can therefore be supposed that straightening in fact occurs in a coordinated manner: each cell perceives its deformation and reacts in order to minimise the curvature.  Thus the plant is endowed with proprioception (1), or an ability to perceive its position at all points along its stem.

By integrating proprioception in their models, the scientists succeeded in reproducing the straightening of eleven species of flowering plants, from tiny wheat sprouts to the trunks of poplar trees.
 
Thus plants are constantly readjusting their habit in response to several types of signals: light, gravity and deformation.  All signals are integrated to enable the coordination of movements.  Further proof then that plants are capable of integrating complex signals and do not just respond as a reflex to a single stimulus, as was still thought recently.
 
(1) Proprioception (from the Latin proprius for "own" and "perception") refers to all receptors, pathways and nerve centres involved in a conscious or unconscious perception of oneself.