Fig. 5. High GA signaling activity correlates positively with growth anisotropy and transverse cell division orientation.

a, b Averaged surface growth (a) and growth anisotropy (b) heat maps (used as proxies for cell expansion intensity and direction, respectively) in the SAM averaged from seven independent plants. c PCA analysis including the following variables: GA signaling, surface growth intensity, surface growth anisotropy, and CLV3 expression. PCA component 1 is mostly associated negatively with surface growth intensity and positively with GA signaling. PCA component 2 is mostly associated positively with surface growth anisotropy and negatively with CLV3 expression. Percentages are the variations explained by each component. d Spearman correlation analysis between GA signaling, surface growth intensity, and surface growth anisotropy at the tissue scale but excluding CZ. The numbers on the right are Spearman’s rho values between two variables. Stars indicate when the correlation/anti-correlation is highly significant. e 3D visualization of Col-0 SAM L1 cells using confocal microscopy. New cell walls formed in the SAM (but not primordia) in 10 h are colored according to their angle values. The color bar is shown in the bottom-right corner. The insert shows the corresponding 3D image at 0 h. The experiment was repeated twice with similar results. f Boxplot representation of cell division frequency in the IPR and non-IPR of Col-0 SAM (n = 10 independent plants). Center lines show the medians and box limits indicate the 25th and 75th percentiles. Whiskers indicate minima and maxima as determined using the R software. P-value is from two-sided Welch’s t-test. g, h schematic diagram showing (g) how the angle of a new cell wall (magenta) relative to the radial direction from the center of the SAM (white dotted line) was measured (only acute angle values, i.e., 0–90°, were considered), and (h) the circumferential/transverse and radial orientations within the meristem. i Frequency histograms of division plane orientation of cells from the entire SAM (dark blue), the IPR (medium blue), and non-IPR (light blue), respectively. P-values are from two-sided Kolmogorov–Smirnov tests. The experiment was repeated twice with similar results. j Frequency histograms of division plane orientation of IPR cells around P₃ (light green), P₄ (mediate green), and P₅ (dark green), respectively. P-values are from two-sided Kolmogorov–Smirnov tests. The experiment was repeated twice with similar results.