Figure 2.

Hypothetical intracellular auxin gradients and root hair position. A, Epidermal cells in trichoblast cell files of the Arabidopsis root produce a root hair toward the rootward end of the cell. This is patterned by a root-tip-high auxin gradient, which is predicted to feed a tip-high intracellular auxin gradient in trichoblasts (blue shading), reinforced by shootward localization of the PIN2 auxin exporter (orange line). B, Triple mutation in aux1 ein2 gn_eb flattens the tip-high auxin gradient and presumably also the intracellular auxin gradient. This is associated with shifts in root hair placement. C, Application of auxin to aux1 ein2 gn_eb mutants shootward of the root hair differentiation zone shifts the root hair position to the shootward end of the cell, presumably associated with an inverted intracellular auxin gradient. D, Application of auxin to aux1 ein2 gn_eb mutants rootward of the root hair differentiation zone restores a more wild-type root hair position, presumably associated with restoration of the tip-high intracellular auxin gradient.