Cellular hypocotyl parameters of trappii mutants under single and additive stress conditions. Seedlings were grown in the light (orange), dark (black), or dark with −0.4 MPa water stress (darkW; blue). (A) Scanning electron micrographs (SEM) of hypocotyls of club-2 mutants. The cell surface area was calculated as the product of cell width and length. club-2 mutants showed, identical to trs120-4 (Fig. 6 B), the opposite hypocotyl cell height and cell surface area adaptations to dark-to-darkW conditions (red asterisks) than the wild-type control (Fig. 6 A). Representative SEM images of seedlings grown under the specified conditions are shown (scale bar = 40 µm). The sample size (n) is given as the number of cells/number of seedlings that were analyzed in gray below the graph. Shown are means ± SD. P values were computed with a two-tailed Student’s t test and are represented as follows: ***: P < 0.001; *****: P < 0.00001. (B–D) Bar plots for a direct comparison of the hypocotyl (B) cell width, (C) cell height, and (D) cell surface area of trappii mutants and the wild-type control (Col-0) shown in Fig. 6, A and B; and Fig. S10 A. The cellular hypocotyl parameters in the light did not significantly differ between trappii mutants and the wild type. club-2 and trs120-4 showed a compromised, but significant adjustment of the cellular parameters under single stress conditions (light to dark). Only under multiple stress (dark to darkW), trappii mutants failed to correctly adjust their cellular hypocotyl parameters with the opposite adjustment of the cell height and surface area compared with the wild type (red letters). Shown are means ± SD. Letters indicate statistical significance in two-way ANOVA with Tukey’s post hoc test. Related to Fig. 6.