Stomatal Conductance and ABA Concentration in the Xylem Sap of Barley Lines of Contrasting Genetic Origins

We investigated the controls of ABA concentration in the xylem sap and of stomatal conductance in five barley ( Hordeum vulgare L.) lines of contrasting origins (Syrian or French), genetic backgrounds and previously field-evaluated drought resistances. Controlled water deficits were applied to young plants in a series of experiments in the greenhouse with contrasting evaporative demands. There was a unique relationship between soil water status and the concentration of ABA in the xylem sap measured at the end of the night. This relationship applied to all experiments for a given line, and was common between lines. Concentrations measured in the sap collected by pressurising leaves were similar to those in the sap of pressurised roots. Stomatal conductance was related to the concentration of ABA in the sap, with relationships which were common for all experiments within each line. Response curves of g s to concentration of ABA in the sap differed among two groups of lines which slightly differed in life cycle duration. Apparent stomatal sensitivity to ABAwas lower in earliest anthesing lines. Both groups comprised lines of either Syrian or French origins, and either ‘drought tolerant’ or ‘drought susceptible’ lines. We conclude that stomatal control had a low genetic variability in the studied range of lines, in spite of the large genetic differences between lines.