Abscisic acid and hydraulic conductivity of maize roots: a study using cell- and root-pressure probes

Using root- and cell-pressure probes, the effects of the stress hormone abscisic acid (ABA) on the water-transport properties of maize roots (Zea maps L.) were examined in order to work out dose and time responses for root hydraulic conductivity. Abscisic acid applied at concentrations of 100-1.000 nM increased the hydraulic conductivity of excised maize roots both at the organ (root Lp(r): factor of 3-4) and the root cell level (cell Lp: factor of 7-27). Effects on the root cortical cells were more pronounced than at the organ level. From the results it was concluded that ABA acts at the plasma-lemma. presumably by an interaction with water channels. Abscisic acid therefore facilitated the cell-to-cell component of transport of water across the root cylinder. Effects on cell Lp were transient and highly specific for the undissociated (+)-cis-trans-ABA. The stress hormone ABA facilitates water uptake into roots as soils start drying. especially under non-transpiring conditions. when the apoplastic path of water transport is largely excluded.