  The hormone auxin is actively transported throughout plants via protein
machineries including the dedicated transporter known as PIN. The associated
transport is ordered with nearby cells driving auxin flux in similar
directions. Here we provide a model of both the auxin transport and of the
dynamics of cellular polarisation based on flux sensing. Our main findings are:
(i) spontaneous intracellular PIN polarisation arises if PIN recycling dynamics
are sufficiently non-linear, (ii) there is no need for an auxin concentration
gradient, and (iii) ordered multi-cellular patterns of PIN polarisation are
favored by molecular noise.
