Physiological changes in grapevine during adjustment to water stress: ABA, leaf gas exchanges and root hydraulic conductivity

Potted grapevine plants cv. Muller Thurgau were grown under control conditions for three months under normal watering, and then a two-week water shortage (Water Stress) was imposed: the initial condition (Control) and the Water Stress were compared, measuring photosynthesis, stomatal conductance, root hydraulic conductivity, leaf ABA, root ABA and xylem sap ABA concentrations. Stomatal behaviour was more correlated with xylem sap ABA than with the concentration of ABA in leaves (total ABA) or in roots. ABA in roots and ABA in leaves were correlated only under water stress conditions. The water stress root signal (xylem sap ABA increase) seems to be important in the early stages of water stress onset. Later, the reduction of RHC and the probable mobilisation of leaf vacuole ABA are more relevant in conditioning stomatal behaviour.