Plant Movement

Plants cannot move from place to place like animals. But they can move certain parts in response to changes around them. This is called plant movement. These movements help plants grow, survive, and respond to their surroundings.

Plant movements are of two main types:

Tropic Movements
Nastic Movements

Tropic Movements

Tropic movements are growth movements that happen in the direction of a stimulus. The stimulus acts on the plant from one side. The movement can be towards or away from the stimulus.

These movements are usually slow and depend on plant growth.

There are different types of tropic movements:

Phototropism – Response to light

In this movement, the plant grows towards the light. This is called positive phototropism. Stems show this movement. If the plant part grows away from light, it is negative phototropism (common in roots). The plant hormone auxin helps in this growth. It moves to the shaded side and makes those cells grow longer. So, the plant bends toward the light.

Chemotropism – Response to chemicals

This is the movement of a plant part toward a chemical. A good example is in plant reproduction. During fertilisation, the ovule (synergids) releases chemicals (LURE peptides). These guide the pollen tube to grow toward the ovule.

Hydrotropism – Response to water

This movement happens when plant roots grow towards water. Roots sense the moisture gradient in the soil and grow in that direction (hydrotropism). That is why we see roots spreading out when we pull up a plant.

Geotropism – Response to gravity

Plant parts also respond to gravity. Roots grow downwards, towards gravity. This is called positive geotropism. Stems grow upwards, away from gravity. This is negative geotropism.

Thigmotropism – Response to touch

This movement happens when a plant part touches something. It is common in climbers and tendrils. They wrap around sticks, wires, or walls for support.

Thermotropism – Response to temperature

This is the growth of plant parts in response to temperature. For example, the flower stalk (peduncle) of Anemone nemorosa grows in response to heat from sunlight.

Nastic Movements

Nastic movements are non-directional. They do not depend on where the stimulus comes from. These movements can happen due to changes in light, temperature, touch, or other factors. Some are caused by growth, while others happen due to changes in turgor pressure in cells.

Here are the main types of nastic movements:

Photonasty – Response to light

Some flowers open and close depending on light intensity. For example, Cestrum nocturnum (opens at night) and Tulip (opens in light).

Nyctinasty – Movements at night or in darkness

These are also called sleep movements. They happen due to changes in the turgor pressure of pulvinus cells. This is controlled by circadian rhythm plus light/dark times. For example, the leaves of clover and oxalis close in the evening and open in the morning.

Thermonasty – Response to temperature

This movement happens due to changes in temperature. Many flowers open or close based on warm or cold conditions.

Seismonasty or Thigmonasty – Response to touch or shock

This movement happens when the plant gets a sudden touch, shock, or vibration. Examples include Mimosa pudica (touch-me-not), which folds its leaves when touched. This is due to the sudden loss of turgor pressure in the motor cells of the pulvinus. Other examples include movement in insectivorous plants or stamens moving when insects land on flowers.

There are other nastic movements too:

Epinasty – downward bending due to faster growth of the upper side
Hyponasty – upward bending due to faster growth of the lower side
Geonasty (or Gravinasty) – response to gravity
Chemonasty – response to chemicals
Hydronasty – response to water

Summary

Plant parts move in response to light, gravity, touch, and temperature. These movements are of two kinds: tropic movements are directional, while nastic movements are not. Such responses help plants survive and grow better. Human activities affect these movements. They use light control, hormone sprays, pruning, watering methods, plant hormones, and physical touch in farming or gardening.

Frequently Asked Questions (FAQs)

Q1. Why do plants move?

A. Plants move to get light, water, and to survive. Movement helps plants live and grow.

Q2. What is chemotropism?

A. Chemotropism is when plants grow toward chemicals. For example, pollen grows toward the ovule. This action is guided by chemical attractants from synergid cells inside the ovule.

Q3. What is the role of auxin in plant movement?

A. Auxin is a chemical in plants. It helps parts grow longer and bend toward light.