FIGURE 2.

Stem tissue sensing and response to gravistimulation by reorientation. In stems, the gravity perceiving cells are located within the endodermis. Upon stimulation from a new gravity vector, the statoliths settle to the lateral side of the cell nearest the gravity vector. The new position of the statoliths leads to a differential increase in auxin concentration in the lateral tissue, and differential growth thereby occurs on the two opposite sides of the stem. This differential growth results in a bending of the stem away from the direction of the gravity vector.