STOMATAL CONDUCTANCE AND ABA CONCENTRATION IN THE XYLEM SAP OF BARLEYLINES 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 previo usly field-evaluated drought resistances; Controlled water deficits we re applied to young plants in a series of experiments in the greenhous e with contrasting evaporative demands. There was a unique relationshi p 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. Concentra tions measured in the sap collected by pressurising leaves were simila r to those in the sap of pressurised roots. Stomatal conductance was r elated to the concentration of ABA in the sap, with relationships whic h 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 stomata l sensitivity to ABA was lower in earliest anthesing lines. Both group s comprised lines of either Syrian or French origins, and either 'drou ght tolerant' or 'drought susceptible' lines. We conclude that stomata l control had a low genetic variability in the studied range of lines, in spite of the large genetic differences between lines.