How do plants respond to gravity?

Plants respond to gravity through a process known as gravitropism, growing roots downwards and shoots upwards.

Gravitropism, also known as geotropism, is the orientation of a plant or other organism in response to gravity. It is a fundamental aspect of plant growth, affecting the direction of root and stem development. The roots exhibit positive gravitropism, meaning they grow in the direction of gravitational pull, which is downwards. This helps the plant to anchor itself in the ground and absorb water and nutrients from the soil.

On the other hand, the shoots of the plant exhibit negative gravitropism. They grow upwards, against the force of gravity. This is crucial for the plant's ability to photosynthesise, as it allows the leaves to reach the sunlight.

The mechanism behind gravitropism involves specialised cells in plant roots and shoots called statocytes. These cells contain tiny, dense particles called statoliths. When the plant's position changes, these statoliths settle to the lower side of the statocyte due to gravity. This movement triggers a signal that leads to the redistribution of a plant hormone called auxin.

Auxin is a key player in plant growth and development. In the context of gravitropism, it accumulates on the lower side of the plant organ. This differential distribution of auxin promotes cell elongation on one side, causing the plant organ to bend towards the source of gravity in roots or away from it in shoots.

In summary, plants respond to gravity through gravitropism, a process that directs their growth and helps them adapt to their environment. This process is regulated by the plant hormone auxin, which is redistributed in response to changes in the plant's orientation relative to the direction of gravity.