The differentiated root of Arabidopsis is characterized by endodermal barriers that are essential for the tight regulation of water and nutrient transport. These barriers correspond to specialized cell wall modifications, Casparian strips, and suberin lamellae, formed at the periphery of endodermal cells. These barriers progressively establish along the root with first Casparian strips (state I of differentiation), and second, the deposition of suberin lamellae (state II of differentiation). It is now well established that Casparian strips form an apoplastic barrier and play an essential role in nutrient homeostasis and that suberin deposition interfere with the coupled trans-cellular pathway. Consequently, only the symplastic pathway is predicted to remain accessible for solutes to reach the inner part of the root in the differentiated root. If our models on plant nutrition highlight the central role of the symplastic pathway for nutrient acquisition in differentiated roots, no functional evidence support this hypothesis. This PhD thesis aimed to study the symplastic pathway: (1) in the context of differentiated roots, (2) along the differentiation gradient, and (3) across the different cell types of the root. This work will provide tools to better understand cell-to-cell communication in differentiated roots and beyond in the context of plant nutrition, as well as signalling or plant defenses.