Fig. 3

Robustness of mechanism with regard to changes in the overall amount of DS (a–c) and molecular noise (d–f). The DS profile on a axial line through the producing cell (*) is indicated in red, the corresponding “readout”, P _{e f f} as a percentage of the intrinsic value, is indicated in cyan. The C5 and pericycle cells are indicated with short and long arrows, respectively. a–c Change of production rate by a factor 2 from the original moves the original profile (solid line) up or down by the same factor everywhere (dashed lines). b Default steady state DS profile. a Half as steep profile. c Twice as steep profile. d–f: Impact of molecular noise dependent on gradient steepness. Noise is illustrated by the lines \([DS] \pm 0.05 \sqrt {[DS]}\). The overall sensitivity (h) and response steepness p are adjusted to keep the primary response curve identical: h=15.797/a.u., p=6 (a, d), h=100/a.u., p=3 (b, e; default) and h=4007.2/a.u., p=1.5 (c, f)