Figure 5. Globally applied exogenous auxins inhibit branch initiation.
(A–D) Branching patterns in wild-type gametophores grown for 5 weeks, immersed for 24 hr in mock (A), 1 μM IAA (B), 100 nM NAA (C) or 1 μM 2,4-D (D) and grown for another 2 weeks. (E–H) mock (E), IAA (F), NAA (G) and 2,4-D (H) treated gametophores before (left) and after (right) removing the leaves, with asterisks indicating lateral branches. Scale bar = 1 mm. (I–K) Bubble plots showed that branch number decreased in response to IAA (I), NAA (J) and 2,4-D (K) compared with mock-treated gametophores. Gametophore length is depicted as the number of metamers and the bubble area is proportional to the number of gametophores with a similar branch number at a particular length. Ordinary least squares regression was used to test whether the relationship between branch number and gametophore leaf number depended on treatment (see ‘Material and methods’), and for (I) the best fitting model was B = (−4.45 + 2.52X) + (0.2 − 0.12X)L meaning that IAA treatment significantly differed from mock treatment (p < 0.01). For (J) the best fitting model was B = (−4.45 + 2.87X) + (0.2 − 0.13X)L; NAA treatment significantly differed from mock treatment (p < 0.001). For (K) the best fitting model was B = (−4.45 + 2.8X) + (0.2 − 0.13X)L; 2,4-D treatment significantly differed from mock treatment (p < 0.001). (L) The apical inhibition zone size increased in response to IAA, NAA and 2,4-D (mean ± SD; bilateral t-test different from mock control, *p < 0.05).