FIGURE 1.

Chemorheological control of wall extensibility. (A) Principle: microfibrils (brown), which in most cases form parallel arrays, are cross-linked by load-bearing (violet) and relaxed (light blue) bonds. The number and strength of the load-bearing bonds determines cell wall strength. Wall extensibility is controlled by chemorheological mechanisms that remove load-bearing bonds. The cell wall relaxes and undergoes turgor-driven mechanical deformation until previously relaxed bonds become load-bearing. (B) Cartoon of cell wall architecture showing microfibrils (brown) and XG chains (green). A small portion of the XG is intertwined or complexed with cellulose, thus sticking the microfibrils together at these points. The endoglucanase Cel12A as well as expansin may act on these relatively inaccessible XG–cellulose interaction domains.