Plant postures are affected by environmental stimuli. When the gravitational direction changes, the Arabidopsis thaliana mutants myosin xif xik (xif xik) and atp-binding cassette b19 (abcb19) exhibit aberrantly enhanced organ bending. Whether their phenotypes are due to the same mechanism is unknown. We characterized the primary root postures of these mutants. Their roots exhibited enhanced gravitropic bending with the same root-tip angles. The wavy roots of vertically grown plants were quantitatively evaluated using four indices. The straightness index (root base-to-tip length to total root-length ratio) was similar for xif xik and abcb19, and it slightly decreased for xif xik abcb19. The curvature index was similar for abcb19 and xif xik abcb19, but it decreased for xif xik, suggesting the ABCB19 deficiency caused the roots to curve more sharply. Combination of these indices for quantitative analyses of root postures may distinguish between similar wavy-root phenotypes and clarify genetic relationships.
