Gene expression in vessel-associated cells upon xylem embolism repair in Vitis vinifera L. petioles

In this work, the involvement of vessel-associated cells in embolism recovery was investigated by studying leaf petiole hydraulics and expression profiles of aquaporins and genes related to sugar metabolism. Two different stress treatments were imposed onto grapevines to induce xylem embolism: one involved a pressure collar applied to the stems, while the other consisted of water deprivation (drought). Embolism formation and repair were monitored during stress application and release (recovery). At the same time, stomatal conductance (g (s)), leaf water potential (I (leaf)) and leaf abscisic acid (ABA) concentration were measured. For each treatment, gene transcript levels were assessed on vessel-associated cells (isolated from leaf petioles by laser microdissection technique) and whole petioles. Both treatments induced severe xylem embolism formation and drops in g (s) and I (leaf) at a lesser degree and with faster recovery in the case of application of the pressure collar. Leaf ABA concentration only increased upon drought and subsequent recovery. Transcripts linked to sugar mobilisation (encoding a beta-amylase and a glucose-6-P transporter) were over-expressed upon stress or recovery, both in vessel-associated cells and whole petioles. However, two aquaporin genes (VvPIP2;1 and VvPIP2;4N) were activated upon stress or recovery only in vessel-associated cells, suggesting a specific effect on embolism refilling. Furthermore, the latter gene was only activated upon drought and subsequent recovery, suggesting that either severe water stress or ABA is required for its regulation.