Stomatal behaviour and water movement through roots of wheat plants treated with abscisic acid

Experiments with isolated roots of wheat plants suggested that when water uptake rates are low, low concentrations of abscisic acid (ABA) may increase the flux of water into roots. This increase was recorded despite an ABA‐stimulated reduction in the hydraulic conductance of the whole root system. Hydraulic conductances were measured under steady‐state conditions. A system is described where the stomatal behaviour and water movement through roots of a single intact plant may be concurrently monitored. Experiments with intact plants confirmed that application of ABA could increase the rate of water movement into roots when uptake rates were low. No such increase was observed at high flux rates. Application of ABA to roots caused partial stomatal closure and caused conductance to oscillate around a reduced mean value. An ABA‐stimulated increase in the turgor sensitivity of stomata is postulated and the significance of this effect is discussed.