Plants orient their organs in response to the gravity vector, with roots growing towards gravity and shoots growing in the opposite direction. The movement of statoliths responding to the inclination relative to the gravity vector is employed for gravity sensing in both plants and animals. However, in plants, the statolith takes the form of a high-density organelle, known as an amyloplast, which settles toward gravity within the gravity sensing cell. Despite the significance of this gravity sensing mechanism, the exact process behind it has eluded scientists for over a century.
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Source: ScienceDaily