geotropismi

Geotropism, or geotropismo, is a directional growth response in plants where growth is guided by gravity. It is a type of tropism in which plant organs orient themselves relative to the gravitational pull. In most plants, roots exhibit positive geotropism, growing downward toward gravity, while shoots display negative geotropism, growing upward away from gravity.

Gravity perception occurs mainly in specialized gravity-sensing cells called statocytes, located in the root cap (columella) and in shoot tissues such as the endodermis. Within these cells, dense amyloplasts act as statoliths that settle under gravity and trigger signaling pathways. The gravity signal is transduced in part by the redistribution of the plant hormone auxin, which regulates differential growth.

In roots, a higher concentration of auxin on the lower side inhibits elongation, causing the root to bend downward toward gravity. In shoots, higher auxin on the lower side promotes elongation, causing the stem to bend upward away from gravity. The resulting curvature arises from differences in cell elongation on opposite sides of the organ.

Geotropism is fundamental to plant development, helping roots explore soil for water and nutrients and shoots to reach light. The term gravitropism is sometimes used interchangeably with geotropism, though some contexts distinguish the concepts as focusing on gravity sensing versus the growth response. Geotropic responses can be studied under gravistimulation or in experiments using clinostats to simulate altered gravity conditions.