Figure 1.

An Auxin Transport Model Predicts Left-Right Auxin Asymmetries.

(A) Screen capture of an auxin transport simulation that recapitulates phyllotactic patterning. Shown are the centers of mass (white lines) and auxin concentration (green lines) of leaf primordia. Primordium cells are highlighted in blue to demonstrate the symmetrical recruitment of cells into the leaf.

(B) There is a significant negative correlation between divergence angle and IAA shift in both C and CC phyllotaxis. The result of such a correlation is that when divergence angles are high, the auxin concentration rests at a more negative angle, and vice versa.

(C) Visualization of the trends in divergence angles and IAA shifts throughout primordium development in C and CC simulations. Note that as primordia develop, they attain extremely negative (C) or positive (CC) values such that auxin falls on the descending side of the primordium. Starting at P3 (indicated with asterisks), IAA shift values become significantly shifted toward the descending direction (see text for significance values).

(D) A DR5 auxin reporter confirms modeled predictions that auxin response is asymmetrically distributed toward the descending side of leaf primordia. (1) Surface reconstructions from a propidium iodide confocal stack. Coloring is based upon surface Gaussian curvature where highly curved domes appear red and creases appear blue. (2) Confocal data showing propidium iodide (cell wall stain) and DR5:VENUSx6 signal (yellow). (3) Total DR5:VENUSx6 signal projected upon surface reconstruction and intensity of DR5 signal indicated by color, where red meristem background indicates no signal. From top to bottom, increasingly older stages of P1 leaf primordia up to P2 are shown. Lines drawn from the tip of the P1 primordium to the center of the meristem indicate the center of the primordium. The descending side of the primordium is indicated to show the excess distribution of auxin response, predominately at the primordium base.