The grapevine VvPIP2;4N aquaporin controls leaf hydraulic capacitance

Our study highlights that leaf hydraulic capacitance (Ch), as well as leaf hydraulic resistance (Rh) are influenced by the constitutive over-expression of VvPIP2;4N aquaporin. Ch in a plant tissue buffers the xylem tension storing and releasing water and has been highlighted in recent years as an important factor that affects water relations such as drought tolerance and embolism formation. Aquaporins are well known to control leaf hydraulic resistance (Rh) but their role in the control of Ch is unknown. Here, we assess Rh and Ch on detached grapevines leaves (cv. Brachetto) wild type (WT) and over-expressing the aquaporin gene VvPIP2;4N (OE). For this purpose, we developed a new method inspired from the pressure-volume curve technique and the rehydration kinetic method, which allowed us to monitor the dynamics of dehydration and rehydration in the same leaf. The recovery after dehydration was measured in the dark, in light non-transpirative conditions, light-transpirative conditions and transpirative condition adding abscisic acid (ABA). Pressurizing leaves in the OE line, the recorded Rh and Ch were respectively lower and higher than those in the WT. The same results were obtained in the dark recovery treatment. In the presence of light, either when leaves transpired or not (by depressing vapour pressure deficit), the described effects disappeared. The change in these hydraulic traits did not affect the kinetics of desiccation of detached leaves in the dark in air, in OE plants compared to WT. The effect of aquaporins on Ch is reported here for the first time and may involve a modulation of cell reflexion coefficient.