Figure 2

Gibberellins negatively regulate RAM size and the longitudinal expansion of cortical cells. (A) Scheme of a Medicago truncatula root and representative examples of wild-type (WT) untreated, GA₃-treated, paclobutrazol (PAC)-treated, and della1 mutant root apices cleared and counterstained with Renaissance to visualize cell walls. The proliferation (PZ) and elongation (EZ) zones are indicated with white lines. Bars = 200 µm. (B,C) Quantification of the PZ size in WT untreated, GA₃-treated, PAC-treated roots (B), and in the della1 mutant (C). (D,E) Quantification of the EZ size in WT untreated, GA₃-treated, PAC-treated (D), and in the della1 mutant (E). (F,G) Quantification of the longitudinal expansion of cortical cells in the EZ in WT untreated, GA₃-treated, PAC-treated (F), and in the della1 mutant (G). (H) Relative expression of MtEXP12 and MtEXP16 in WT roots after a CK (BAP) treatment preceded or not by a GA₃ treatment. Transcript levels are normalized relative to the MtACTIN11 reference gene and calibrated relative to mock-treated roots (the dotted line indicating a ratio of 1). In (B–G), 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). In (H), error bars represent standard deviation.