Figure 1. IAA application on pin1 meristem leads to local tissue softening and pectin de-methyl-esterification in sub-epidermal tissues.

(A) IAA induced organ formation in a pin1 mutant inflorescence apex (t = 72 h post application). Apparent Young's modulus (E_A, or 'rigidity') map of a representative pin1 meristem ∼18 hours post IAA application as determined with a 1 µm (B) or 5 µm (C) spherical tip. Total number of meristems analyzed + IAA, n = 13. Each pixel in a rigidity map corresponds to the E_A value obtained from one indentation point. (D) Graphical display of averaged E_A data from all meristems with values for meristem (black bars) and just above application site (white bars). Significant difference indicated by asterisk at p-value<0.01 (T-test on averages from n meristems: ‘pin1–IAA’ 5 µm n = 6 and 1 µm n = 7 (p-values 0.71 and 0.57 respectively), ‘pin1+IAA’ n = 13 (p-values: 1 µm p = 0.02, 5 µm p = 2.2E-5). Error bars are propagated standard deviations). Non-averaged results for all meristems can be found in Figure S1 (displaying reduced rigidity: 1 µm, +Inactive IAA n = 0/7, +IAA n = 1/13. 5 µm, +Inactive IAA n = 3/7, +IAA n = 13/13). (E,F) Topographical reconstruction of measured surfaces, as estimated by AFM point-of-contact, with the rigidity maps of (B,C) respectively used to color the surface. Note that meristem curvature does not correlate with areas of decreased E_A, and that there is no bulging of the meristem accompanying decreased rigidity. (G) Serial transverse sections showing 2F4 labeling of HG de-methyl-esterification in a representative pin1 meristem ∼18 hours after IAA application (n = 9). M: meristem, as: application site, Scale bars  = 100 µm (A,G) or 10 µm (B,C). Asterisk in (G) indicates 2F4 labeling in sub-epidermal tissues. Statistics in Figure S2, control data in Figure S3.