Definition of Tropisms and Nastias

The tropisms They are responses that involve growth directed towards the stimulus: the plant grows towards the direction of the stimulus to get closer to it or tries to move away by growing in the opposite direction. Tropisms always imply growth, therefore, tropisms are irreversible. For example, if a plant grows towards the light, the stem curvature that occurs cannot be reversed. If you change the light source, the plant will curl again.

The nastias, on the other hand, are temporary and reversible responses, which do not imply growth, but do imply movement. Some examples of nastias are the opening and closing of flowers during the day and night.

Plants, like animals, have response mechanisms to stimuli, despite their processes are slower because they do not have neural networks organized in a nervous transmission system fast. These responses are mediated by chemical signaling systems, a plant endocrine system, and are known as tropisms and nasties.

Tropisms

One of the most distinctive features of tropisms is growth in a specific direction: plants can grow toward the stimulus (positive tropism) or move away from it (negative tropism). By allowing them to grow toward beneficial resources, such as light or water, or away from adverse conditions, plants can maximize their survival and growth.

Most tropisms are mediated by chemical regulators: the plant hormones or phytohormones. exist various types of tropisms, each of which is related to a specific environmental stimulus and a particular growth direction.

Phototropism

It is the directional response of plants to light. In the case of positive phototropism, plants grow towards the light source, allowing them to make the most of the light to drive photosynthesis.

Stems have positive phototropism. This means that the stem will rise in search of the light source, and if the light comes from one side, the stem will curve towards that side.

Phototropism is mediated by a plant hormone called auxin, which accumulates on the side of the stem that does not receive light and causes that side to grow more, thus producing a curvature in the stem in the direction of the light source.

Geotropism or gravitropism

In this case, the stimulus that triggers growth is the force of gravity. When the plant germinates, the root grows seeking to bury itself, while the stem grows upward. This occurs because the plant detects the direction of the force of gravity and the light source.

Roots have positive geotropism, since they grow downward, in the direction of gravity, to anchor themselves in the soil and search for water and nutrients.

In stems geotropism is negative, which allows the aerial parts of the plant to grow upward, against gravity, to reach the light.

Geotropism is also regulated by the distribution of auxin. In some plant cells, located at the tip of the root and in the stem, there are starch “granules”, which are like miniature grains of sand. These granules are called amyloplasts and they are attracted by gravity, like anything on Earth.

Amyloplasts are deposited in the lowest part of the cell; just like the sand in a water bottle will fall to the bottom of the bottle. So, the cell can tell which side is down and which side is up. This reception triggers gravitropism.

Hydrotropism

Plant roots can also grow towards wetter areas detecting soil moisture: they have positive hydrotropism.
It is still not entirely clear how roots detect moisture or what physiological mechanisms trigger tropism.

This process is essential for the survival of the plant, since it guarantees that the roots extend in search of water.

Chemotropism

It is the response of plants to chemical substances present in the soil, such as mineral salts or organic compounds.

The roots can show positive chemotropism towards beneficial substances and negative chemotropism towards toxic substances. This ensures that the plant grows in areas where it can obtain the necessary nutrients and avoids harmful areas.

Thigmotropism

Thigmotropism is the plant response to mechanical contact. Some plant species can show a positive thigmotropism, growing towards the object that touches them, or a negative thigmotropism, moving away from contact.

This phenomenon can be seen in the vines and climbing plants, which have positive thigmotropism and they use it to grow and wrap around support structures. When the stem of the plant touches a rigid object, it begins to grow around it.

Characteristics and aspects of nastias

Nastias, unlike tropisms, are Fast movements, which can occur in seconds and are reversible.

The photonasty refers to the response of plants to changes in the length of day and night, which affects flowering and other processes. This type of daily movements can be seen in some flowers, which open during the day and close at night, or vice versa. Some plants, such as clovers and other legumes, fold their leaves at night and expand them during the day to take advantage of the light.

The thigmonasty It is the response of plants to touch. Some plants, such as the mimosa (Mimosa pudica) or certain carnivorous plants, such as those of the flytrap family (Droseraceae family) react to touch by closing their leaves; either to protect itself from herbivores in the case of mimosa or to trap insects.

Unlike thigmotropism, Mimosa leaves can reopen (the nastias are reversible) but the coiled stem of a vine cannot uncoil, it has already grown with that shape.

Importance of tropisms in Plant Biology

Tropisms play an essential role in plant biology and have important implications in ecology and agriculture. They allow plants to optimize the uptake of essential resources, such as light, water and nutrients. This gives them a competitive advantage in their environment and allows them to survive and grow more efficiently.