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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 to the wind: touch

INRA scientists have demonstrated the crucial role of the wind in regulating plant growth, showing that it has a major impact on crop or forest yields.  They have modelled this phenomenon in order to predict the resistance of plants to lodging or fracture.

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

When you look at a cultivated field, all the plants are of a relatively homogeneous height.  Similarly, forest canopies are characterised by a dominant height.  How is it possible to explain this phenomenon, when behaviours can differ markedly following seed germination, resulting in discrepancies that may be considerable? Bruno Moulia gives two explanations: "firstly, the plant "sees" its neighbour by capturing the dark red light it reflects, at any point on the stem.  So if it is taller than its neighbour, the top of its stem no longer captures dark red, which gives it a perception of its own height (see Part 2). Secondly, a taller plant is more exposed to the wind, whose effect is to slow down its growth in height".  This dual perception allows plants in a field or a forest to grow in a relatively coordinated manner.

 Wind as a regulator of growth

  Alfalfa surrounded by netting that prevents it from moving with the wind grows higher than in the open field.. © INRA, Bruno Moulia
Alfalfa surrounded by netting that prevents it from moving with the wind grows higher than in the open field. © INRA, Bruno Moulia
As early as 2005, Bruno Moulia's team observed that alfalfa surrounded by netting that prevented it from moving with the wind grew higher than in the open field.  "If we continue to protect it from the wind by raising the height of the netting as the plants grow, it will continue to grow without stopping",  explained the scientist.  Under natural conditions, the wind can restrict the growth of a plant by a factor of between 0 and 50%, with important consequences with respect to yield.  Plants become tougher in the wind: they adapt their height as a function of their wind exposure, so the stronger the winds, the shorter they will grow.

The reasons underlying wind sensitivity

Scientists have established that like animals, plants perceive the wind through a mechanical deformation of their cells.  The "pressure" of the wind distorts the cell membrane and acts on the mechanically sensitive channels that activate ionic currents.  Within a few seconds, the stimulus propagates towards growth zones via a process analogous to a nerve impulse.  It appears that there is also a hydraulic component, a pressure wave transmitted via xylem.  Finally, using transcriptomic methods, the researchers have shown that this response to wind modifies the expression of around 2000 to 3000 genes, and they have identified the initial regulating factors.

A model to predict wind susceptibility

 Based on knowledge acquired on the mechanisms underlying plant responses to wind, scientists have developed a model that integrates the different stages: distortion by the wind, perception by the plant, signalling to growth zones and finally the response of growth zones.  This model can predict the quantities and positions of the genes thus expressed, and at the whole plant level can predict growth in terms of height and diameter.  A collaborative project with the Joint Research Unit for Forest and Wood Resource Studies (UMR 1092, LERFOB) in Nancy is now trying to apply this model to the beech, in order to  contribute to anticipating the risks of fractures in trees.

The height of rose bushes is regulated by bars that pass regularly over the plants to bend them, thus imitating the effect of the wind.. © INRA, Bruno Moulia
The height of rose bushes is regulated by bars that pass regularly over the plants to bend them, thus imitating the effect of the wind. © INRA, Bruno Moulia

 

In horticultural greenhouses in Angers that are by definition sheltered from the wind, scientists and their professional partners are developing systems to restrict the growth of plants.  Bars or straps are regularly passed over the plants to bend their stems, thus imitating the effect of the wind and enabling the control of their height growth and ramification.

 

(1) LERFoB: UMR1092 LERFoB Joint Research Unit for Forest and Wood Resource Studies, INRA Nancy.

Nerve impulses do exist in plants

As early as the 1900s, the Indian biologist Chandra Bose demonstrated the existence of electrical signals in plants.  He measured a response analogous to the action potential of a neuron after stimulating a leaf of the sensitive plant, Mimosa pudica (1).  Although plants do not have any nerves, plant cells can transmit electrical signals comparable to the nerve impulses of animals.  Phloem, which carries sap, may thus constitute a sort of major axon.  Plant equivalents to animal synapses (structures that allow a nerve impulse to move from one neuron to another) are not yet known, but plants produce structures analogous to neurotransmitters such as GABA.

(1) Mimosa pudica is a small tropical plant that folds its leaves within a few seconds of being touched.

Plants communicate what they perceive

A rosette of Arabidopsis thaliana.. © INRA, MEDIENE Safia
A rosette of Arabidopsis thaliana. © INRA, MEDIENE Safia

A series of studies conducted separately within and outside INRA have reached the conclusion that plants transmit their perception of the wind to their neighbours.  Indeed, plants neighbouring a plant that receives the wind will also stop growing in height, within the next 30 minutes.  This transmission is achieved via the emission of ethylene, a hormone that is mobilised in stressful situations.

Bruno Moulia reports other studies that have illustrated communication between plants:  Arabidopsis rosettes that grow next to each other finally touch according to a specific behaviour: the leaves of one rosette become erect, which results in that plant becoming visible to its neighbour by emitting dark red light.  The plants therefore have plenty of time to move away from each other.  "The plant perceives this contact and delivers a warning message, like a red card, inviting the others to keep their distance.  I assimilate this to a hint of a sign, which offers numerous ideas for research" concludes the scientist.