A putative role for TIP and PIP aquaporins in dynamics of leaf hydraulic and stomatal conductances in grapevine under water stress and re-watering

We examined the role of aquaporins (AQPs) in regulating leaf hydraulic conductance (Kleaf) in Vitis vinifera L. (cv Chardonnay) by studying effects of AQP inhibitors, and AQP gene expression during water stress (WS) and recovery (REC). Kleaf was measured after 3h of petiole perfusion with different solutions and to introduce inhibitors. The addition of 0.1mm HgCl2 to 15mm KCl reduced Kleaf compared with perfusion in 15mM KNO3 or KCl, and these solutions were used for leaves from control, WS and REC plants. Perfusion for 3h did not significantly alter stomatal conductance (gs) though expression of VvTIP1;1 was increased. WS decreased Kleaf by about 30% and was correlated with gs. The expression of VvTIP2;1 and VvPIP2;1 correlated with Kleaf, and VvTIP2;1 was highly correlated with gs. There was no association between the expression of particular AQPs during WS and REC and inhibition of Kleaf by HgCl2; however, HgCl2 treatment itself increased expression of VvPIP2;3 and decreased expression of VvPIP2;1. Inhibition by HgCl2 of Kleaf only at early stages of WS and then after REC suggested that apoplasmic pathways become more important during WS. This was confirmed using fluorescent dyes confined to apoplasm or preferentially accumulated in symplasm.