Functional Water Flow Pathways and Hydraulic Regulation in the Xylem Network of Arabidopsis

In vascular plants, the xylem network constitutes a complexmicrofluidic system. The relationship between vascularnetwork architecture and functional hydraulic regulationduring actual water flow remains unexplored. Here, wedeveloped a method to visualize individual xylem vesselsof the 3D xylem network of Arabidopsis thaliana, and toanalyze the functional activities of these vessels using syn-chrotronX-raycomputedtomographywithhydrophilicgoldnanoparticles as flowtracers. We showhow the organizationof the xylem network changes dynamically throughout theplant, and reveal how the elementary units of this transportsystem are organized to ensure both long-distance axialwater transport and local lateral water transport. Xylemvessels form distinct clusters that operate as functionalunits, and the activity of these units, which determineswater flow pathways, is modulated not only by varying thenumber and size of xylem vessels, but also by altering theirinterconnectivity and spatial arrangement. Based on thesefindings, we propose a regulatory model of water transportthat ensures hydraulic efficiency and safety.Keywords: Arabidopsis thaliana Gold nanoparticle Hydraulic regulation Synchrotron X-ray CT Water trans-port Xylem network.Abbreviations: AuNP, gold nanoparticle; DAB, days afterbolting; SEM, scanning electron microscopy; SXRCT, synchro-tron X-ray computed tomography; VB, vascular bundle.