title: Long-distance abscisic acid signalling under different vertical soil moisture gradients depends on bulk root water potential and average soil water content in the root zone.
abstract: To determine how root-to-shoot abscisic acid (ABA) signalling is regulated by vertical soil moisture gradients, root ABA concentration ([ABA](root)), the fraction of root water uptake from, and root water potential of different parts of the root zone, along with bulk root water potential, were measured to test various predictive models of root xylem ABA concentration [RX-ABA](sap). Beans (Phaseolus vulgaris L. cv. Nassau) were grown in soil columns and received different irrigation treatments (top and basal watering, and withholding water for varying lengths of time) to induce different vertical soil moisture gradients. Root water uptake was measured at four positions within the column by continuously recording volumetric soil water content (θv). Average θv was inversely related to bulk root water potential (Ψ(root)). In turn, Ψ(root) was correlated with both average [ABA](root) and [RX-ABA](sap). Despite large gradients in θv, [ABA](root) and root water potential was homogenous within the root zone. Consequently, unlike some split-root studies, root water uptake fraction from layers with different soil moisture did not influence xylem sap (ABA). This suggests two different patterns of ABA signalling, depending on how soil moisture heterogeneity is distributed within the root zone, which might have implications for implementing water-saving irrigation techniques.
authors: The Lancaster Environment Centre, Lancaster University, Lancaster, Lancashire, LA1 4YQ, UK. j.puertolas@lancaster.ac.uk
authors: Jaime
authors: J
authors: Puértolas
authors: Rosalía
authors: R
authors: Alcobendas
authors: Juan J
authors: JJ
authors: Alarcón
authors: Ian C
authors: IC
authors: Dodd
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism*; D003681:Dehydration; D027805:Phaseolus / Q000378:metabolism / Q000502:physiology*; D010937:Plant Growth Regulators / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism / Q000502:physiology; D018517:Plant Roots / Q000378:metabolism / Q000502:physiology; D018520:Plant Shoots / Q000378:metabolism / Q000502:physiology; D018526:Plant Transpiration / Q000502:physiology*; D015398:Signal Transduction; D012987:Soil / Q000737:chemistry; D014867:Water / Q000378:metabolism*; D052584:Xylem / Q000378:metabolism / Q000502:physiology
chemical_list: D010937:Plant Growth Regulators; D012987:Soil; D014867:Water; D000040:Abscisic Acid
keywords: Phaseolus vulgaris; partial root zone drying; root-to-shoot signalling; soil moisture heterogeneity