Blanc SVSE 7 - Sciences de la vie, de la santé et des écosystèmes : Biodiversité, évolution des écosystèmes, écosystèmes productifs, agronomie

Biophysical and molecular determinisms of tree vulnerability to embolism – PitBulles

Biophysical and molecular determinants of vulnerability to embolism in trees

The circulation of water in the tree takes place under tension, that is to say in a condition physically metastable and subject to the risk of cavitation. Vulnerability to cavitation is a major feature of the drought resistance of trees.

Identify the molecular players of cavitation

Identify the molecular basis of cavitation is a major challenge for genetic improvement and protection of woody species in a changing climate. The objective of this project is to understand the key factors that control the vulnerability of xylem to cavitation. The main hypothesis underlying this project is that the mechanism of cavitation is determined by the structure and physico-chemical properties of the primary pit wall .

The approach is to define the anatomical structures critical to the formation of cavitation in the aim of identifying the genes coding for these structures. A central part of this project is to analyze these properties for species, genotypes and phenotypes contrasting vis-à-vis their vulnerability to embolism. These studies on the fine structure of punctuation form the basis of an analysis of micro-fluidic operation.

The project is mid-term, the results are still under acquisition. Some significant progresses have been achieved on the structural, mechanical and chemical compositions of pits. This helped develop a first mechanical model of the pit and cavitation.
Moreover, genes putatively involved in resistance to cavitation have been identified and are under validation

The short-term outlook is validation of putative gene for cavitation and analysis of a biomimetic model of the structure of pits.

5 publications

Climate change will affect the sustainability of forest ecosystems, which will result in strong ecological and economical repercussions. Water availability being of the main factors limiting the functioning of today’s forests, the increasing risk of extreme droughts will be a the most disturbing climatic factor. A major challenge for research is to provide relevant and operational criteria in order to identify genotypes more resistant to climatic hazards. Our project aims at fulfilling this task.
In trees, sap transport operates under very negative hydrostatic pressures, especially when exposed to water stress. Because water is in a metastable condition, trees are living under the risk of a sudden vaporization of their sap, namely the risk of embolism. The work done over the last two decades on the hydraulic performance of trees led to the significant conclusion that resistance to embolism is a major adaptive trait for tree to drought tolerance. However, studies on the genetic diversity and on the ecological implications of this trait are still very limited, for two reasons. Firstly, some studies were not feasible because no technique allowed the analysis of this trait on a large number of individuals. The development of the "Cavitron" technique by the coordinator of this project has recently lifted this methodological difficulty. In contrast, the genetic basis of resistance to embolism remains unknown to this day, which greatly hampers research in the fields of molecular ecology or population genetics. The aim of this project is to lift this second pitfall.

The approach we have put in place is to identify anatomical structures critical to the formation of emboli in the objective to identify genes coding for these structures. In the current state of knowledge, embolism spreads in the vascular tissue of trees where a bubble of air enters through the walls of the conduits at the level of a pit, the anatomical structure allowing the passage of the sap from one conduit to another. The main assumption underlying this project is that the mechanism of embolism induction is determined by the structure and physico-chemical properties of the primary pit wall. A central part of this project is to analyze, with the most modern techniques available, these properties for species, genotypes and phenotypes contrasted regarding their vulnerability to embolism. Particular attention will be paid on the wall pectic composition because preliminary results demonstrate their key role in this mechanism. The work on the fine structure of pits will form the basis of a micro-fluidic analysis of their function. The idea is to propose a physical model explaining the mechanism of embolism. This model will be validated by experiments on biomimetic artificial walls. Following these investigations, we will be able to offer a targeted list of specific genes coding for the key structures of the pits and putatively involved in resistance to embolism. The final component of this project is to validate the involvement of these genes using the tools of molecular biology.

The project is built on the interdisciplinarity and complementarily of three partners, each of them being leader in key areas for this study: tree hydraulics, plant primary wall, diphasic fluid mechanics. This interdisciplinary approach proposed here for the first time is expected to solve major scientific pitfalls and open new doors to innovative research on forest genetic resources.

Project coordinator

Monsieur Herve COCHARD (INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE - CENTRE DE RECHERCHE DE CLERMONT FERRAND THEIX) – cochard@clermont.inra.fr

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

IMFT INSTITUT NATIONAL POLYTECHNIQUE DE TOULOUSE
INRA INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE - CENTRE DE RECHERCHE DE CLERMONT FERRAND THEIX
INRA INSTITUT NATIONAL DE LA RECHERCHE AGRONOMIQUE - CENTRE DE RECHERCHE DE NANTES

Help of the ANR 599,991 euros
Beginning and duration of the scientific project: - 48 Months

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