Figure 1.

(A) Schematic of the model root showing the radial discretization used to represent the different root tissue types (from outermost region to innermost region: the epidermis, cortex, endodermis, pericycle, and xylem). The purple and red cylinders show the location of the CS and SL, respectively. (B) Schematic longitudinal cross-section of the model root. The light gray lines show the radial and axial discretization. The different tissue types are highlighted by different colors, while the extent of different developmental zones (EZ and DZ) are indicated by arrows. Some of the model boundary conditions are also indicated. For visual clarity, the z and r axes are scaled differently. (C) Expanded view of a small section of the root cross-section in (B) showing the location of a passage cell. The z and r axes are here drawn to the same scale (refer to the scale bar) highlighting the actual relative axial to radial proportions. The blue arrows indicate ion fluxes. In (B,C), vertical purple lines indicate the location of the CS, vertical red lines represent SL and yellow lines represent functional xylem. Purple dashed lines indicate incomplete CS while yellow dashed lines represent the transition from non-functional to functional xylem. The root dimensions are given in Table 1. The coordinate system (r, z) is as shown in (A). Gravity force is in the direction of decreasing z.