Movement in Plants

Plants exhibit various forms of movement, although these movements may not be as easily noticeable as those in animals. Higher plants primarily display bending, twisting, elongation, and other similar movements in response to specific stimuli.

Types of Plant Movements

There are two main types of movements in plants:

AUTOMATIC MOVEMENTS

PARATONIC MOVEMENTS

Automatic Movements

Automatic movements refer to the movements that occur due to inherent factors within the plant itself. These movements can be further classified into two types:

Locomotion Movement and Growth Movement

Locomotion Movement: This type of movement involves the movement of the entire plant body, specific organs, or materials within plant cells. Examples include the streaming movement of protoplasm, chromosome movement during cell division, ciliary movement, flagellary movement, etc.

Growth Movement: Growth movements involve changes in the form and shape of plant organs. These movements are a result of unequal growth on different sides of organs such as stems, roots, tendrils, buds, etc. There are three types of growth movements:

Epinasty: The upper surface of a bud exhibits more growth compared to the lower surface, causing the buds to open. Leaves and petals also show epinastic movement.

Hyponasty: When the growth on the lower surface of a leaf in bud condition is more pronounced than on the upper surface, the bud remains closed.

Nutation: The apex of a plant undergoes zigzag growth due to alternating changes in growth rate on opposite sides. This movement is known as nutation. When the apex rotates around an axis during its growth, it is called circumnutation.

Thigmotropism

PARATONIC MOVEMENTS

Paratonic movements are responses to external stimuli and occur due to factors outside the plant. These movements can be classified into three types:

TACTIC MOVEMENT

TROPIC MOVEMENT

NASTIC MOVEMENT

Tactic Movement

Tactic movements occur in response to specific external stimuli and can be either positive or negative. These movements are related to locomotion and are categorized based on the nature of the stimulus.

Phototactic Movement: This movement is a response to light, such as the passive movement of chloroplasts due to cyclosis.

Chemotactic Movement: This movement occurs in response to chemicals. For example, the movement of sperm cells in liverworts, mosses, and ferns towards the archegonia in response to nucleic acid released by the ovum.

Phototropism

Tropic Movement

Tropic movements are curvature movements caused by stimuli coming from one side. These movements depend on the direction of the stimulus and occur in one direction due to differences in the growth rate of the two sides of the organ. Examples of tropic movements include:

Phototropism: Movement in response to light, resulting from differential growth in the root or stem.

Thigmotropism: Movement in response to touch. When vines come into contact with a solid object, the growth on the opposite side of the contact increases, causing the tendril to coil around the support.

Chemotropism: Movement in response to chemicals. This can be observed in the hyphae of fungi.

Hydrotropism: Movement in response to water. Roots exhibit positive hydrotropism, growing towards water sources.

Geotropism: Also known as gravitropism, this movement is in response to gravity. Roots display positive geotropism (growing towards gravity), while shoots exhibit negative geotropism (growing against gravity).

Sleep movement in Prayer Plant

NASTIC MOVEMENT

Nastic movements are non-directional movements in response to stimuli. They can be further classified into different types:

Nyctinasty: These movements occur in response to external stimuli and lead to differential growth. Nyctinasty can be divided into two types:

Photonasty: Movement due to changes in light intensity, causing flowers to open and close.

Thermonasty: Movement due to temperature changes, causing upward and inward bending of petals, resulting in the closing of tulip flowers at night.

Haptonasty: This movement occurs in response to contact with external objects. A notable example is the closing action of the Venus flytrap.

Seismonastic or Turgor Movement: This movement is a result of changes in turgor pressure caused by shaking or pressure. It can be observed in sleep movements and rapid movement of leaflets.

SLEEP MOVEMENT

Certain plants raise their leaves in the morning and lower them in the evening. This phenomenon, known as sleep movement, can be observed in plants like beans, Sylvia, and some members of the legume family. The swollen portion of the petiole, called the pulvinus, plays a crucial role in sleep movements. Daily changes in turgor pressure within the pulvinus cause the leaves to raise or lower their position.

RAPID MOVEMENT OF LEAFLETS

Mimosa Pudica, also known as the "touch me not" plant, exhibits rapid movement of its leaflets. When stimulated, the main petiole falls, the secondary petioles close together, and leaflets fold toward each other in pairs. This movement is caused by differential loss of turgor pressure on the two sides of the pulvinus. The plant regains turgor after a few minutes, restoring the leaf's upright position.