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 shoots parallel to the pull of gravity, high concentration of auxin moves towards the bottom side of the root to stimulate elongation of the bottom cells, while suppressing cell growth on the top of the shoot. This allows the bottom cells of the shoot to continue a curved growth and elongate its cells upward with the auxin, opposite the pull of gravity as the auxin move towards the bottom of the root.
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