Hydraulic conductivity of detached shoots of Vitis vinifera L. vines overexpressing the grape aquaporin gene VvPIP2;4N.

Hydraulic conductivity of detached grapevine shoots overexpressing VvPIP2;4N was assessed during a 30-minutes period either submerging the basal cut of the shoot under water or letting the shoot to transpire in air. We used detached shoots to avoid both root and root-to-shoot signalling effects on water transport, due to VvPIP2;4N aquaporin root activity. The measurement in free air caused embolism, reducing hydraulic conductivity. When shoots were detached from irrigated plants, both embolism extent and shoot transpiration, the cause of embolism formation in air-transpiring shoots, were higher in transgenic shoots than in wild type controls. However, when measurements were performed on in vivo embolized shoots (i.e. detached from droughted plants), the in-air embolism formation of transgenic shoots decreased as in wild type controls. In addition, hydraulic conductivity of the droughted shoots absorbing water increased more in transgenic than in wild type shoots, showing a VvPIP2;4N-dependent embolism repair during water absorption. These results show that a drought-derived signal controls drought embolism and activates embolism repair in VvPIP2;4N overexpressing shoots.