Contrasting the time-scales for maximum reestablishment in the different mechanisms. Computer simulations were performed for the (A): source-decay; (B): unidirectional transport; and (C): reflux-loop mechanism. Simulations are done as described in Figure 5. The simulations are initiated with the steady state morphogen distribution. At t=0 the morphogen influx ceases and the QC cells, containing the maximum, are removed. Graphs show morphogen profiles along a longitudinal cross-section through a vascular cell file at different time points, indicated by the colours. (A1) With high decay rates, the source-decay mechanism presents a dramatic disappearance of the morphogen in the root tip after ablation of the source: all morphogen disappears within 5 min. (A2) In contrast, with slow morphogen diffusion, the source-decay mechanism maintains a maximum over long time-scales (15 days). However, especially in in the vicinity of the removed source, the slope fades out within a few hours. (B) The gradient of the unidirectional transport mechanism remains unaffected by the disappearance of the maximum. On a short time-scale all cells maintain the same concentration. Due to the auxin decay and interruption of the influx, auxin values decrease homogeneously over the whole tissue on a longer time-scale, such that the new ‘maximum’ continues to diminish in magnitude. (C) In the reflux-loop mechanism there is a quick reestablishment of an auxin maximum, with a small region just above the removed maximum presenting a fold increase in auxin concentrations. On a longer time-scale the overall concentrations decrease due to auxin decay and lack of influx, bringing down the absolute level of the maximum.