Accumulation rate of ABA in detached maize roots correlates with root water potential regardless of age and branching order

How much ABA can be supplied by the roots is a key issue for modelling the ABA-mediated influence of drought on shoot physiology. We quantified accumu lation rates of ABA (S-ABA) in maize roots that were detached from well-wat ered plants and dehydrated to various extents by air-drying. S-ABA was esti mated from changes in ABA content in root segments incubated at constant re lative water content (RWC). Categories of root segments, differing in age a nd branching order, were compared (root branches, and nodal roots subdivide d into root tips, subapical unbranched sections, and mature sections), All categories of roots accumulated ABA, including turgid and mature tissues co ntaining no apex. S-ABA measured in turgid roots changed with root age and among root categories, This variability was largely accounted for by differ ences in water content among different categories of turgid roots. The resp onse of S-ABA to changes in root water potential (Psi(root)) induced by deh ydration was common to root tips, nodal roots and branches of several ages, while this was not the case if root dehydration was expressed in terms of RWC. Differences among root categories in the response of S-ABA to RWC were due to different RWC values among categories at a given Psi(root), and not to differences in the response of S-ABA to Psi(root).