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The management of water stress by the root system of plants

Through their roots, plants can perceive different soil parameters such as water and oxygen content or nutrient levels. In response to variations in these parameters, plants can then adjust their root water uptake. INRA and CNRS, working in collaboration with Syngenta, have revealed a mechanism by which plants adapt to water stress. These findings open new opportunities for selection.

Le stand INRA au Salon International de l'Agriculture 2015 (21 février - 1er mars). Un Rhizotron est un outil permettant de visualiser l'architecture racinaire d'une plante, ici une légumineuse.. © INRA, NICOLAS Bertrand
Updated on 03/17/2017
Published on 11/25/2016

The behaviour of plants challenged by water stress

In most plants affected by flooding and hence hypoxia (lack of oxygen), water absorption via the roots is regulated negatively and results in leaf wilting and the closure of stomata. In parallel, the absorption of macronutrients (nitrogen, phosphate and potassium) is inhibited. In the event of water deficit (drought), roots continuously adjust their growth and water absorption capacity in order to maintain plant water status. The mechanisms linking soil properties to root hydraulics in these different contexts are still poorly understood.
 

HydroRoot: a project to address how plants use water

The absorption of water by plants is determined by several factors: 1) environmental conditions (drought, floods, soil nutrient availability, etc., (2) root architecture and anatomical characteristics (endodermal barriers, size of xylem vessels), and (3) the activity of aquaporins, "water channel" proteins which facilitate the passage of water through cell membranes. To understand the mechanisms that control the hydraulic conductivity of tissues, the scientists have coupled hydraulic phenotyping, quantitative genetics and mathematical modelling using the model plant Arabidopsis thaliana.

The role of aquaporins and the identification of genes involved in water transport

To unravel the genetic foundations of root water transport, the scientists first focused on candidate genes. They analysed genotypes that were altered in the function of aquaporins, or in the differentiation of the endodermal barrier or xylem. These studies revealed in particular the crucial role of lignin deposits in the endodermis. Other mutants and the mathematical modelling of root water transport, showed that axial hydraulic conductance (through xylem vessels) is strongly dependent on root architecture. Radial water flows, on the other hand, are dependent on aquaporins, whose function is inhibited under abiotic stress conditions.

Potassium levels and the detection of oxygen: parameters governing root hydraulics

The quantitative genetics approach revealed the HCR1 gene, which codes for a protein kinase of the MAP3K family. HCR1 acts as a negative regulator of root water transport and the activity of root aquaporins. It is linked to the response of roots to hypoxia, in relation to external potassium availability. By integrating these two signals, the HCR1 gene modulates the resilience of plants to different flooding scenarios: the plants can thereby integrate opportunities for subsequent growth linked to the presence of nutrients in the soil.

These findings provide innovative foundations for the development of genetic and agrochemical strategies that will target the central regulators of root hydraulics in cultivated plants. Hydraulic modelling of the roots, coupled with genetic approaches, also suggest the possibility of more efficient phenotyping in the field and the selection of genotypes adapted to drought.

Contact(s)
Scientific contact(s):

  • Christophe Maurel (04 99 61 20 11) INRA-CNRS-Montpellier SupAgro-Université de Montpellier Joint Research Unit for Biochemistry and Plant Molecular Physiology (UMR-0386, B&PMP). INRA, 2 Place Viala 34 060 Montpellier cedex 2
Associated Division(s):
Plant Biology and Breeding
Associated Centre(s):
Occitanie-Montpellier

Sources

  • Zaigham Shahzad, Mathieu Canut, Colette Tournaire-Roux, Alexandre Martinière, Yann Boursiac, Olivier Loudet, Christophe Maurel, « A potassium-dependent oxygen sensing pathway regulates plant root hydraulics», Cell, 167, 87-98, september 22,2016.