Biophysical and molecular determinants of vulnerability to cavitation in young poplars

Trees acclimate to changing environment. Water transport occurs under negative pressure from the roots to the leaves in the vascular system of the xylem. During water stress, the level of negative pressure can increase drastically and lead to the rupture of the water column. This cavitation event can be critical for the tree. Vulnerability to cavitation (VC) is a highly variable hydraulic trait that depends on the specie and the growing conditions. The anatomical parameters that drive the phenomena are still unknow. Actually, researches focus on the pits structures that are the hydraulic pathway between vessels. In this work, we investigated the impact of different growth conditions on pit structure of young poplars and the relationship with the VC. Xylem formed under stress conditions was analyzed using a multidisciplinary approach: - Ecophysiology: stomatal conductance, transpiration, leaf water potential, VC, primary and secondary growth were measured. - Wood anatomy was investigated at the tissue and cell wall level by optical and TEM microscopy. This approach was associated with X-ray microtomography observations to characterize the spatial distribution of cavitation. - Molecular analysis: We hypothezed that genes involved in VC may be involved in the biosynthesis of the cell wall and pits. We investigated the local transcriptome of the tissues. Preliminary results showed lower stomatal conductance, transpiration and leaf water potential for stressed plants than control plants. X-ray microtomography observations indicated that wood formed under water stress condition is more resistant to embolism. We will discuss the relationship between growth speed and VC.