Table 1. Notations.

$𝓖=(V,E)$	Graph of node set V and of edge set E.
${𝓖}^{*}=(V^{*},E^{*})$	Oriented sub-graph of node set V* and of oriented edge set E*.
I* = V∖V*	Set of isolated cells of $\overline{𝓖}$.
i ∼ j	Neighbouring cells i and j with (i, j) ∈ E.
M = ∣V∣	Number of nodes of the graph $𝓖$.
${\mathcal{N}}_i$	Neighbourhood of cell i, that is ${\mathcal{N}}_i=\{k\in V|k~i\}$.
d i	Number of neighbours of cell i, i.e. $d_i=\left|{\mathcal{N}}_i\right|$.
m	Number of membranes of the graph $𝓖$, i.e. m = |E|.
a i	Auxin concentration in cell i.
a ij	Auxin concentration in the membrane of cell i facing cell j.
P i	PIN concentration in cell i.
p ij	PIN concentration on the membrane of cell i facing cell j.
V i	Volume of cell i.
S ij	Surface area of the membrane separating cell i from cell j.
W	Ratio of the surface area of membrane ij to the cell volume, when the cells are regular.
$J_{i\to j}^D$	Auxin flux through the membrane between cell i and j due the diffusion.
$J_{i\to j}^A$	Auxin flux through the membrane between cell i and j due the PIN active transport.
J i → j	$J_{i\to j}^D+J_{i\to j}^A=$ net flux through the membrane ij.
γ D	Auxin diffusion rate.
γ A	Auxin active transport rate.
D	Normalized auxin diffusion rate.
T	Normalized active transport rate.
${\alpha }_a^i$	Auxin synthesis rate in cell i.
${\beta }_a^i$	Auxin degradation rate in cell i.
${\alpha }_p^i$	PIN production rate in cell i.
${\beta }_p^i$	PIN degradation rate in cell i.
κ	Saturating constant.
μ	Background PIN removal rate from the membranes.
λ	PIN insertion rate in the membrane ij.
h	Non-linear response function.
Φ(x)	= h(x/W).