Plants do not have a nervous system, but they can detect the direction of gravity and adjust growth. In many plants, dense starch-filled organelles called statoliths settle inside specialized cells when the organ is tilted. That shift is linked to signals involving the hormone auxin, which changes how cells grow. Roots typically bend downward, while shoots grow upward, although light and other cues also influence direction.
Gravity-sensitive cells
When a root or shoot is turned, small dense bodies called statoliths can shift within gravity-sensing cells. In roots these bodies are amyloplasts, which contain starch. NASA describes statoliths as part of the way plants perceive gravity. [1]
The cell does not need to ‘know’ where down is. The physical settling of the organelles provides a directional cue that the plant’s signalling system can use.
From a cue to a bend
Gravity perception is followed by signalling inside the plant. Auxin, a plant hormone, is redistributed across the organ. In roots and shoots, unequal auxin responses cause cells on opposite sides to grow at different rates, curving the organ. Roots generally show positive gravitropism, growing with gravity; shoots show negative gravitropism, growing against it. [2]
The response unfolds over time. A seedling placed on its side may first grow sideways, then gradually curve as growth on each side changes.
Gravity is one cue among several
Light can pull a shoot toward a window, while gravity provides another directional signal. Water, touch and the plant’s developmental stage also affect growth. The final shape reflects how these cues interact, not a single on-off switch.
NASA studies gravity perception because plant growth in space and on other worlds depends on how roots and shoots respond when the gravity environment changes. [3]
Sources and evidence
- NASA — Plant Gravity Perception ↗
Statoliths and the research question of how plants sense gravity.
- NASA Technical Reports Server — Mechanisms of early plant gravitropism ↗
Perception, signalling and growth response in gravitropism.
- NASA — TROPI-2 plant biology experiment ↗
Definition of gravitropism and relevance to fractional gravity.
Sources consulted: 11 October 2026. Written with AI assistance and checked against the linked references; not independently reviewed by a subject specialist. Sources do not endorse this article. See our editorial policy.
Revision: Original explanatory article prepared from linked scientific and institutional sources; scope and uncertainty are stated in the text.