Figure 8.

Gravitropism of tt4 Mutants and tt4 mdr4 Double Mutants.

(A) Total angle of wild-type, tt4, and tt4 mdr4 roots accruing over time following reorientation. The hypertropism of mdr4 prevailed over the hypotropism of tt4 in the tt4 mdr4 double mutant, indicating that mdr4 is epistatic to tt4, consistent with flavonoids being endogenous regulators of MDR4-dependent auxin transport. Shown are the mean values [MSOffice2] of 16 individuals for the wild type, six for tt4, and six for tt4 mdr4. Angle was determined from electronic images acquired every 2 min. The se indicated by error bars every 15 min.

(B) Spatiotemporal distribution of gravitropic curvature of Col-0 wild-type roots.

(C) Spatiotemporal distribution of gravitropic curvature of tt4 roots. Gravitropic curvature is weaker and shifted apically compared with the wild type in tt4 mutants.

(D) Spatiotemporal distribution of gravitropic curvature of tt4 mdr4 roots. The basal shift in the spatial distribution of curvature due to the mdr4 mutation is shown to be epistatic to the opposite effect of the tt4 mutation, as was the effect on total angle in (A). The black contour line surrounds the region that differs from the tt4 single mutant response to a statistically significant degree (P = 0.05).