Comparison of GA sensitivity in roots and above-ground tissues of A. thaliana and lettuce, low temperature tolerance of root elongation, and a model of GID1 evolution. (A and B) Inhibitory effect of ancymidol on hypocotyl (A) or root (B) elongation in A. thaliana gid1 mutants, gid1a-1 [background ecotype: Nossen (nos)], gid1b (nos), and gid1c [Columbia (col)]. (C) Recovery of Arabidopsis gid1 roots stunted by 3 × 10−7 M ancymidol by GA4. (D) Inhibitory effect of ancymidol on the elongation of root, hypocotyl, and leaf in lettuce. (E) Recovery of lettuce root stunted by 3 × 10−6 M ancymidol by GA4. (F) Effect of low temperature on A. thaliana gid1 root elongation. The root length of each genotype at 22 °C was set to 1. Error bars indicate SD. n ≥ 4. **P < 0.01 based on two-sided Student’s t test. n.s., not significant, P > 0.05. Actual root lengths are shown in SI Appendix, Fig. S19. (G) Model for the establishment and improvement of the GID1 receptor during plant evolution (for details, see text).