Fig. 2
Systematic exploration of response parameters h and p. a, b Effects of changing h (a) and p b on the response (reduction of P eff ). Overall sensitivity h moves the location where P eff is reduced by 50 %, which always occurs at a concentration of 1/h (a). Response steepness p does not affect this point, but changes the steepness of the response (b). c–e P eff (in cyan) as percentage of the intrinsic (starting) value as a readout of the axial DS profile through the signaling epidermal cell (*). The steady state DS profile is indicated in red, on a logarithmic scale. Short and long arrows indicate the C5 and pericycle layers, respectively, on both sides of the vascular tissue. c Changing DS production by a factor 3 up/down. Line types match DS profile and P eff response. d Changing h by a factor 3 up/down. Note that this has the same effect on the readout as changing the amount of DS by the same factor. e Changing p. Defaults: h=100/a.u., p=3. f Snapshots of auxin concentrations at T = 1 hour for a wide range of p and h values. Default parameter values are indicated with a green border and reasonable values with a yellow border. For comparability, auxin concentration range for all figures is 0 - 2.5 C v . Where relevant, the white contours occur at 5 C v (regular) and 25 C v (bold). For full ranges, see Additional file 9: Figure S3. Note that not all segments have reached steady state, although the DS gradients have. g, h Contour plots of [IAA] = 5 C v auxin concentration boundary at T = 30 hours with p=3 (g), or h=100/a.u. (h) fixed. Note that increasing h (with constant p) can move the boundary arbitrarily far away from the DS producing epidermal cell in the middle of the root segment (g), whereas with increasing p (with constant h) the far end of the boundary saturates (h). For additional contours, see Additional file 9: Figure S4