Exodermal suberin contributes to ion homeostasis and growth in potato

Most angiosperm roots develop two apoplastic barriers: the endodermis and the exodermis. Although the exodermis is widespread among angiosperms, its functional role remains comparatively poorly understood. Here, we studied root apoplastic barrier formation in potato (Solanum tuberosum). Using histochemical staining, we mapped the spatiotemporal deposition of lignin/poly(phenolic) material and suberin in the endodermis and the exodermis. The exodermis develops an outer polar lignin/poly(phenolic) cap and rapidly establishes a continuous suberized layer close to the root tip, whereas endodermal cells form Casparian strips first and suberize later and discontinuously. The early and continuous suberization of the exodermis suggests a potential role in regulating the radial movement of mineral nutrients. To explore this possibility, we analyzed plants down-regulating the suberin biosynthetic gene CYP86A33, which showed a 61% reduction in root suberin content. Suberin-deficient plants displayed altered element concentration and reduced growth. In addition, micro-particle-induced X-ray emission (micro-PIXE) analyses provided spatial information of elemental distribution within the roots and highlighted anatomical compartments defined by apoplastic barriers. Together, these results support the contribution of exodermal suberin to ion homeostasis and plant growth, and provide new insights into the role of root barriers in mineral nutrient regulation in a major crop species.