Understanding xylem refilling: molecular and physiological perspectives

Water transport in xylem lumens of terrestrial plants occurs in metastable state sustained by cohesion forces among water molecules. Formation of embolism (expansion of vapour voids in the conduits) in such condition can permanently block upward water movement as air bubbles filling lumens break the column continuity and the transition of cohesion forces. Failure of plant hydraulic conductivity negatively affects transpiration and this can result in reduction of photosynthetic activity, drought-related tissue damage and ultimately plant death. Trees have evolved several mechanisms to mitigate the loss of water transport capacity and it has been demonstrated that many plant species counter embolism formation with a fast recovery processes that can occur despite the presence of moderate tension. Currently, we lack a full understanding of the biology behind the refilling process, although several proposals and comprehensive hypotheses of how this might happen have been investigated and proposed.

The major goal of this project is to understand changes in biological activity of xylem parenchyma cells induced by the formation of embolisms in xylem vessels. These changes result in the generation of the osmotic gradients, which drive water into empty vessels. In order to achieve this goal, different molecular and physiological approaches will be used and the presented objectives are being investigated:

• Determination of the signal triggering a cellular response to embolism formation.
• Elucidation of refilling physiology including analysis of cellular microenvironment properties (pH, osmotic potential, ionic concentration and composition), membrane transport activity (transport of carbohydrates, ions and water), and enzymatic activity (cellulosic and apoplastic metabolism of carbohydrate).
• Expression analysis of genes involved in metabolism pathways during the onset of embolism and embolism refilling.
• Elucidation of the role of aquaporins as a source of water in the refilling process using transgenic plants.

Principal investigator: Francesca Secchi

Project start October 2014, duration 36 months

Financial support: Young Scientists Program “Rita Levi Montalcini', Ministry of Education, University and Research (MIUR)