Alignment between PIN1 Polarity and Microtubule Orientation in the Shoot Apical Meristem Reveals a Tight Coupling between Morphogenesis and Auxin Transport
Figure 5
Microtubule and PIN1 behavior when cellulose synthesis is inhibited with isoxaben.
(A) Surface of a clv3-2 GFP-MBD meristem before isoxaben treatment, with magnified insert (later time points after treatment shown in [C] and [D]). Note the presence of strong GFP signal on all sides for many of the cells, indicating a random alignment of microtubules in those cells. Scale bar: 20 µm. (B) Theoretical impact of isoxaben on patterns of stress (red) and strain (green) in a cylindrical pressure vessel. The main direction of stress in a cylindrical pressure vessel is circumferential. As plant cells reinforce their walls parallel to the main stress, the residual axial stress drives a strain perpendicular to the main stress. If cellulose deposition is inhibited, the strain follows the stress pattern, i.e., the circumferential strain becomes higher than the axial strain. (C) Impact of isoxaben on microtubule behavior in the clv3-2 GFP-MBD line at different time points after application (microtubule arrangements before application are shown in [A]). Cell growth continues, and microtubules gradually form thick bundles. There is no apparent coordination in the orientations. The red dot marks the same cell at the three time points. Scale bar: 40 µm. (D) Close-ups from (C) showing microtubule orientations in relation to the cell shapes after isoxaben treatment. (E) Surface of a GFP-MBD meristem 70 h after the isoxaben treatment. Note the presence of circumferential bundles of microtubules. Scale bar: 20 µm. (F) Close-up from (E) showing that the microtubules become circumferential even at the tip of the meristem, and this can be correlated to the dome shape of the meristem in the wild-type background. The red dotted lines represent the position of the anticlinal walls (reconstructed from sections through the stack). Scale bar: 10 µm. (G) Surface of a meristem expressing PIN1-GFP before and 20 h after isoxaben treatment. The GFP signal becomes localized to a subdomain of the plasma membrane. Scale bar: 30 µm. (H) Close-ups from (G): the GFP signal is concentrated on the circumferential membrane near a vertex. (I) Surface of a meristem expressing PIN1-GFP 16 h after isoxaben treatment, showing a preferential localization of PIN1 on the circumferential membranes.