ARABIDOPSIS-THALIANA SKU MUTANT SEEDLINGS SHOW EXAGGERATED SURFACE-DEPENDENT ALTERATION IN ROOT-GROWTH VECTOR

Roots of wild-type Arabidopsis thaliana seedlings in the Wassilewskija (WS) and Landsberg erecta (Ler) ecotypes often grow aslant on vertica l agar surfaces. Slanted root growth always occurs to the right of the gravity vector when the root is viewed through the agar surface, and is not observed in the Columbia ecotype. Right-slanted root growth is surface-dependent and does not result directly from directional enviro nmental stimuli or gradients in the plane of skewing. We have isolated two partially dominant mutations in WS (sku1 and sku2) that show an e xaggerated right-slanting root-growth phenotype on agar surfaces. The right-slanting root-growth phenotype of wild-type and mutant roots is not the result of diagravitropism or of an alteration in root gravitro pism. It is accompanied by a left-handed rotation of the root about it s axis within the elongation zone, the rate of which positively correl ates with the degree of right-slanted curvature. Our data suggest that the right-slanting root growth phenotype results from an endogenous s tructural asymmetry that expresses itself by a directional root-tip ro tation.