Growth, in particular reorganization of the root system architecture, mineral homeostasis and root hormone distribution were studied in Arabidopsis thaliana upon copper excess. Five-week-old Arabidopsis plants growing in hydroponics were exposed to different Cu(2+) concentrations (up to 5 muM). Root biomass was more severely inhibited than shoot biomass and Cu was mainly retained in roots. Cu(2+) excess also induced important changes in the ionome. In roots, Mg, Ca, Fe and Zn concentrations increased, whereas K and S decreased. Shoot K, Ca, P, and Mn concentrations decreased upon Cu(2+) exposure. Further, experiments with seedlings vertically grown on agar were carried out to investigate the root architecture changes. Increasing Cu(2+) concentrations (up to 50 muM) reduced the primary root growth and increased the density of short lateral roots. Experiment of split-root system emphasized a local toxicity of Cu(2+) on the root system. Observations of GUS reporter lines suggested changes in auxin and cytokinin accumulations and in mitotic activity within the primary and secondary root tips treated with Cu(2+). At toxic Cu(2+) concentrations (50 muM), these responses were accompanied by higher root apical meristem death. Contrary to previous reports, growth on high Cu(2+) did not induce an ethylene production. Finally lignin deposition was detected in Cu(2+)-treated roots, probably impacting on the translocation of nutrients. The effects on mineral profile, hormonal status, mitotic activity, cell viability and lignin deposition changes on the Cu(2+)-induced reorganization of the root system architecture are discussed.