Fig. S6.

Diagram of the model of node I. The dynamics of Si in the node is simulated by using a diffusion equation on the 2D grids. A cell unit has 5 × 10 grids. The PCB is represented by three cell layers. The three cells of PCB are connected by symplast region (assuming plasmodesmata). At the symplast and apoplast regions (red and blue regions), Si diffuses freely at a rate determined by specific diffusion coefficients. Across the symplast and apoplast regions (plasma membrane), Si moves via transporters (but we assumed a low permeability of the cell membrane itself). At the xylem site (brown region), Si moves toward the panicle or the flag leaf (upper direction) according to an advection–diffusion equation.