A comparison of root and shoot hydraulics, aquaporin expression and leaf gas exchange between two grapevine cultivars reveals differences in hydraulic control mediated by aquaporins

Abstract

Hydraulics of plants that take different strategies of stomatal control under water stress are still relatively poorly understood. Here we explore how root and shoot hydraulics, gas exchange, aquaporin expression and abscisic acid (ABA) concentration in leaf xylem sap ([ABA]xylem) may be involved and coordinated. A comparison in responses to mild water stress and ABA application was made between two cultivars of Vitis vinifera L. previously classified as isohydric (Grenache) and anisohydric (Syrah). Grenache showed stronger adjustments of leaf, plant, and root hydraulic conductances to decreased soil moisture and a steeper correlation of stomatal conductance (gs) to [ABA]xylem than Syrah resulting in greater conservation of soil moisture, but not necessarily more isohydric behaviour. Under well-watered conditions, changes in vapour pressure deficit (VPD) had a strong influence on gs in both cultivars with adjustments of leaf hydraulic conductance. Grenache was more sensitive to decreases in soil water availability compared to Syrah that rather responded to VPD. There were stronger correlations between plant hydraulic parameters and changes in aquaporin gene expression in leaves and roots of Grenache. Overall, the results reinforce the hypothesis that both hydraulic and chemical signals significantly contribute to the differences in water conservation behaviours of the two cultivars.