Gravitropism, the process of plant roots growing in the direction of gravity and plant shoots growing opposite of gravity, is dependent on the location and concentration of auxin in the roots and shoots. In roots not parallel to the pull of gravity, high concentration of auxin moves towards the bottom side of the root to suppress growth of the bottom cells, while allowing cell elongation on the top of the root. This allows the top cells of the root to continue a curved growth and elongate its cells downward with little auxin, towards the pull of gravity as the auxin move towards the bottom of the root.
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