Primary root elongation rate as a function of root tip (apical 10 mm, encompassing the elongation zone) ABA content for various maize genotypes growing in vermiculite at high water potential (yw) (0.03 MPa, open symbols) or low water potential (1.6 MPa, closed symbols). At high water potential, the root ABA content of hybrid (cv.
FR27 3 FRMo17) seedlings was raised above the normal level by adding various concentrations of ABA (A) to the vermiculite. At low water potential, the root ABA content was decreased below the normal level by treatment with fluridone (F) or by using the vp5 or vp14 mutants. Data are plotted as a percentage of the rate for the same genotype at high water potential. Elongation rates of the mutants at high water potential were similar to their respective wild types (from Sharp, 2001; reprinted with permission of Blackwell Science; original data from Saab et al., 1990, Sharp et al., 1994 and unpublished data of I-J Cho, B-C Tan, DR McCarty, and RE Sharp).