Establishment of embryonic axis foreshadows the main body axis of both adult plants and animals, but underlying mechanisms are considered distinct. Plants utilize directional, cell-to-cell transport of the growth hormone auxin to generate an asymmetric auxin response that specifies embryonic apical-basal axis. The auxin flow directionality depends on the polarized subcellular localization of PIN-FORMED (PIN) auxin transporters. It remains unknown, which mechanisms and spatial cues guide cell polarization and axis orientation in early embryos. I will present novel insights into the formation of embryonic axis in Arabidopsis by the identification of a crucial role of the local tryptophan-dependent auxin biosynthesis. My talk will discuss how precise spatio-temporal control of distinct auxin sources provides a necessary, non-cell autonomous trigger for coordinated cell polarization and subsequent apical-basal axis orientation during embryogenesis, and presumably also other polarization events during postembryonic plant life.