Figure 10.

Schematic Diagram of the Statolith-Mediated Force Transduction to the Cortical ER in Gravity-Sensing Columella Cells.

(A) Before reorientation the ER is compressed by the weight of the statoliths.

(B) Reorientation leads to a rapid displacement of the statoliths away from the ER interface toward the central cytoplasm. This elastic rebound can potentially trigger an initial Ca²⁺ or other signal within the columella cell.

(C) The statoliths sediment driven by the gravitational force (g) until contact with the cortical ER adjacent to the new lower cell wall is reestablished.

(D) During the sedimentation phase, the statoliths interact transiently with the cortical ER through direct physical impacts and constantly through a cytosol-mediated action at a distance (dashed line), which may also reach the subtending plasma membrane. These mechanisms are postulated to activate mechanosensitive sites in the ER and/or at the plasma membrane—here exemplary shown is a Ca²⁺ response. N, nucleus.