Auxin and gravitopism
Geotropisms
Gravitropism (also called geotropism) is a response of plant roots to the stimulus of The force of attraction between all objects. The more mass an object has, the larger the force of gravity it exerts.. They grow downwards as a result of gravity.
Plants responses to gravity:
- when the stem grows against the force of gravity, this is known as a negative geotropism
- when a root grows in the direction of the force of gravity, this is known as a positive geotropism
Just like phototropism, geotropism is also caused by an unequal distribution of auxin.
In a root placed horizontally, the bottom side contains more auxin and grows less - causing the root to grow in the direction of the force of gravity.
The opposite happens in a stem. When a stem is placed horizontally, the bottom side contains more auxin and grows more - causing the stem to grow upwards against the force of gravity.