Figure 3

Gibberellins negatively regulate the radial expansion of cortical cells and the number of cortical cell layers. (A) Representative confocal optical transversal section of wild-type (WT) untreated, GA₃-treated, paclobutrazol (PAC)-treated, and della1 mutant root apices cleared and counterstained with Renaissance to visualize cell walls. Bars = 50 µm. (B,C) Quantification of the root diameter in WT untreated, GA₃-treated, PAC-treated roots (B), and in the della1 mutant (C). (D,E) Quantification of the radial expansion of outer cortical cells in the elongation zone (EZ), in WT untreated, GA₃-treated, PAC-treated roots (D), and in the della1 mutant (E). (F,G) Ratio between the longitudinal expansion and the radial expansion of outer cortical cells in the EZ in WT untreated, GA₃-treated, PAC-treated roots (F), and in the della1 mutant (G). (H,I) Quantification of the number of cortical layers in WT untreated, GA₃-treated, PAC-treated roots (H), and in the della1 mutant (I). (J) Representative example of the stem cell niche organization in WT untreated, GA₃-treated, and PAC-treated root apices. Colored dots highlight the different cell files from the outside to the inside: epidermis (blue), cortex (green), and endodermis (orange). Bars = 100 µm. In (B–I), measurements were made two weeks post-germination. Error bars represent confidence interval (α = 0.05; n > 5 plants) of one representative biological experiment out of two, and asterisks indicate significant differences between the untreated control and treated samples, or WT and mutants, based on a Mann-Whitney test (α = 0.05).