Abstract
Higher plants reorient their growth direction by sensing the organ tilt relative to the direction of gravity (gravitropism). Historically famous “the starch statolith hypothesis” has explained how plants sense their organ tilt, that is, starch accumulating amyloplasts with high density sink like stones along the gravity vector in the cell, and then trigger subsequent signalings. Recent molecular genetic studies suggest that the sedimentation of amyloplasts is not a spontaneous event but is controlled by actin filaments and vacuolar membranes. This review mainly focuses on the mechanisms of gravity perception involving the amyloplasts movement and following signaling events during gravitropism.
