Structural requirements of abscisic acid (ABA) and its impact on water flow during radial transport of ABA analogues through maize roots

The effect of (+) (ABA) and (-)-abscisic acid and nine ABA metabolites, precursors or derivatives on radial water movement through maize roots, was investigated using a suction technique (Freundl and others 1998). (+)-ABA, (+)- and (-)-abscisyl aldehyde, (+)-8'-hydroxymethyl ABA, (+)-8'-methylene, and (+)-8'-acetylene ABA stimulated radial water transport. (-)-ABA, phaseic acid, and (+)-8'-acetylene methyl ABA were ineffective. ELISA analysis for ABA detected and apparent increase of free ABA(xyl) in xylem sap of excised root systems that were perfused with either (+)-abscisyl aldehyde, (+)-8'-methylene, (+)8'-acetylene-ABA, or ABA-glucose ester. The analogues (+)-8'-hydroxymethyl ABA and (-)-abscisyl aldehyde passed the cortex of maize roots without changing the ABA(xyl). The data from this Study permit conclusions about the structural requirements for hormonal regulation of hydraulic conductivity.