Geotropism: What is, types and examples in plants

Geotropism, also called gravitropism, is a type of directional growth of plants in response to gravity. This characteristic is even manifested by bowing a plant, where roots and outbreaks readjust their growth direction according to gravitational force. This process is common in both upper and many lower plants, and even in some fungi.

Its mechanism is based on an unequal auxin distribution: on the roots, the lower side with more auxin grows less, causing a curvature down; The opposite occurs in the stems, growing more that side and orienting up.

We recommend knowing more about tropism: what is, types and examples, where geotropism is included.

It can be positive or negative:

Positive geotropism

Positive geotropism occurs when a part of the plant grows in the same direction as gravity, that is, down. The clearest example is the growth of the roots, which, upon receiving more auxin on its lower side, inhibit their elongation in that area, causing a descending curvature.

They also have positive geotropism some modified stems, such as ginger rhizomes and potato tubers, which grow underground. In addition, certain flowers such as peanuts extend their peduncle after fertilization and bury it, developing the fruits underground through Geocarpia.

Negative geotropism

Negative geotropism refers to the growth of plant organs in the opposite direction to gravity, that is, up. This type of response is mainly observed in stems and branches, which must overcome gravitational force to guide its leaves and flowers towards the light. In these cases, auxin accumulates on the lower side of the stem, promoting greater cell elongation in that area and generating an ascending curvature.

Some underground organs also have negative geotropism. The pneumorrizas, respiratory roots of mangroves such as Avicennia Germinans and Racy LagunculariaThey grow up to facilitate the exchange of gases in saturated water soils.

Geotropism works through a complex interaction between gravity, plant hormones and specialized cellular structures. When a plant is placed sideways, the auxin hormone accumulates in the lower part of the stem due to gravity. This accumulation stimulates greater cell elongation on that side, making the stem bend up. On the other hand, in the roots, auxin inhibits growth in the lower part, causing them to curve down.

The main severity sensor in plants are the statolites, dense amyloplasts that store starch and settle at the base of the specialized cells called statocites. These statolites are present in roots, stems and inflorescences, and their active sedimentation typical typical channels that trigger auxiliary redistribution.

• Root: These grow in the direction of gravity due to the accumulation of auxin in the lower part of the root, which inhibits its growth in that area and allows elongation at the top. Here you can learn about the root parts and their functions.
• Brokes: Geotropism acts oppositely. Auxina accumulates at the bottom of the outbreak, stimulating cell elongation in that region, which causes the outbreak to curve up, moving away from gravity.
• Fruit: In the case of bananas, being exposed to light, auxin migrates to the shading side of the fruit, which stimulates the differential growth of their cells and produces its characteristic ascending curvature, which also responds to gravity. In this other post you can know the parts of the fruit and their functions.

• Geotropism is essential for plants to adjust their growth in response to gravity, since they cannot move like other organisms.
• Thanks to this mechanism, the roots are oriented down to absorb water and minerals, which also contributes to the stability of the plant.
• The outbreaks develop contrary to gravity to better capture sunlight, facilitating photosynthesis, flowering and fruiting.
• This process is regulated by auxin, a phytormone that promotes or inhibits cell elongation according to its concentration and location. Examples such as soy hypochotilos demonstrate how the asymmetric distribution of active auxin specific genes (Sours) that induce the curvature of the outbreaks. At the cellular level, amyloplasts act as gravity sensors when moving within specialized cells, activating mechanisms that are not yet completely understood.

If you want to read more articles similar to geotropism: what is, types and examples in plants, we recommend that you enter our biology category.