Autonomic Movements in Plants in Detail

 Autonomic Movements in Plants:

These are the movements shown by plants and plant organs and organelles. These are spontaneous movements due to some internal cause in response to an external stimulus. There are the following types of autonomic movements in plants:

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1. Tactic Movements:

• Definition: Tactic movements are the directional responses of plants to external stimuli in which the whole plant, plant organ, or organelle moves in response to an external stimulus.
• a. Phototactic Movements:
  • Definition: Phototactic movements are responses to light.
    • i. Positive Phototactic Movements:
      • Definition: Positive phototactic movements involve the plant moving towards the source of light.
      • Example with Explanation: Sunflowers exhibit positive phototactic movements. The flower heads follow the sun throughout the day, ensuring optimal exposure to sunlight for photosynthesis. This enhances the plant's ability to generate energy. Cyclosis is another example of positive phototactic movements. The internal cause is that the chloroplast moves towards the sunlight to fix more carbon dioxide, so it moves towards the light source.
    • ii. Negative Phototactic Movements:
      • Definition: Negative phototactic movements involve the plant moving away from the source of light.
      • Example with Explanation: Some fungi show negative phototactic movements. In response to light, certain fungal spores move away to find a more suitable environment for growth and reproduction. In high-light intensity, the choroplast moves away from light and moves in cyclosis.

2. Turgor Movements:

• Definition: Turgor movements are reversible changes in the turgor pressure of cells, leading to alterations in the shape or position of plant organs.
  • a. Sleep Movements:
    • Definition: Sleep movements are rhythmic changes in the position of plant organs, often associated with the daily light-dark cycle.
    • Example with Explanation: Mimosa pudica, also known as the sensitive plant, displays sleep movements. Its leaflets fold upward in the evening and reopen during the day. This is a protective mechanism to conserve water and reduce exposure to herbivores during the night.

    • Structure and Function of Pulvinus in Plants

      The pulvinus is a fascinating and specialized structure found in certain plants, serving unique functions related to movement and adaptability. Let's delve into its structure and the key functions it performs:

      Structure of Pulvinus:

      The pulvinus is typically located at the base of leaflets or leaf segments and is composed of specialized tissues that enable its distinctive features.

      1. Motor Cells:

         • The pulvinus contains specialized cells known as motor cells. These cells play a crucial role in the rapid movements associated with the pulvinus. They undergo changes in turgor pressure, leading to the reversible expansion and contraction of the pulvinus.

      2. Parenchymatous Tissue:

         • Parenchyma cells, a type of simple plant tissue, make up the pulvinus. These cells are relatively unspecialized and have thin cell walls, contributing to the flexibility required for movement.

      3. Vascular Bundles:

         • Vascular bundles, including xylem and phloem, are present in the pulvinus. They facilitate the transport of water, nutrients, and signaling molecules, which are essential for the coordination of movement.

      4. Intercellular Spaces:

         • Intercellular spaces within the pulvinus allow for the movement of water, ions, and gases. These spaces contribute to the dynamic changes in turgor pressure, a key factor in the pulvinus's ability to undergo reversible movements.

      Function of Pulvinus:

      1. Rapid Movements:

         • The primary function of the pulvinus is to enable rapid and reversible movements in response to external stimuli. This could include mechanical stimuli, such as touch, or environmental cues like changes in light or temperature.

      2. Leaf Orientation:

         • Plants with pulvini use these structures to adjust the orientation of leaves or leaflets. This adaptation allows the plant to optimize its exposure to sunlight, contributing to efficient photosynthesis.

      3. Protective Response:

         • In some cases, the pulvinus-driven movements serve a protective role. For example, in Mimosa pudica, the folding of leaflets during the evening or in response to touch is a defensive mechanism to deter herbivores and conserve water.

      4. Environmental Adaptation:

         • The pulvinus helps plants adapt to their environment by responding to specific stimuli. This responsiveness allows plants to navigate challenges, such as avoiding excessive sunlight or responding to physical disturbances.
  • b. Rapid Movement of Leaflets:
    • Definition: Rapid leaf movements are quick responses to stimuli, often facilitated by changes in turgor pressure.
    • Example with Explanation: The Venus flytrap exhibits rapid movements of its leaflets. When triggered by the touch of an insect, the trap closes rapidly, capturing and digesting the prey. This movement is crucial for the plant's nutrient acquisition.

    • Rapid Movement of Leaflets in Leguminous Plants: Unveiling Nature's Dynamic Choreography

      Leguminous plants, a diverse family including well-known members like Mimosa pudica, exhibit a captivating botanical ballet through their rapid movement of leaflets. This phenomenon, often referred to as "seismonastic movement," is a remarkable display of nature's dynamic response mechanisms. Let's delve into the intricacies of this rapid movement and its significance for leguminous plants.

      The Mechanism:

      1. Pulvinus as the Conductor:

         • At the heart of this rapid movement is the pulvinus, a specialized joint located at the base of the leaflet. The pulvinus acts as the conductor, orchestrating the movement through changes in turgor pressure within its cells.

      2. Motor Cells in Action:

         • Motor cells within the pulvinus play a pivotal role. When stimulated by touch or other mechanical forces, these cells undergo rapid changes in turgor pressure. This prompts the pulvinus to either collapse or expand, leading to the swift folding or unfolding of the leaflet.

      Mimosa pudica: A Star Performer

      Leaf-Folding Extravaganza:

      • Perhaps the most famous leguminous plant showcasing rapid leaflet movement is Mimosa pudica, also known as the sensitive plant. Upon physical touch or disturbance, the leaflets of Mimosa pudica fold inward rapidly, creating a mesmerizing display.

      Defensive Ballet:

      • The rapid leaflet movement in Mimosa pudica serves as a defensive mechanism. By folding its leaves, the plant deters herbivores and reduces the surface area vulnerable to potential threats. It's a dance of self-preservation in response to perceived danger.

3. Growth Movements:

• Definition: Growth movements are changes in the orientation or position of plant organs that result from differential growth rates in different parts of the organ.
• Epinasty:
  • Definition: Epinasty is a growth movement where the upper surface of a leaf grows faster than the lower surface, causing the leaf to bend downward.
  • Example with Explanation: In response to certain environmental factors, such as high humidity or ethylene exposure, some flower petals may exhibit epinasty. This movement can enhance pollen release and facilitate pollination.
• Hyponasty:
  • Definition: Hyponasty is a growth movement where the lower surface of a leaf grows faster than the upper surface, causing the leaf to bend upward.
  • Example with Explanation: In certain plants, hyponasty occurs during the initial stages of leaf development, helping the young leaves to unfold and expand, optimizing their exposure to light.
• Nutation:
• Definition: Nutation is a growth movement characterized by a bending or spiraling motion, often observed in growing stems or tendrils.
• Example with Explanation: Twining plants, like morning glories, exhibit nutational movements. As they grow, they spiral around a support structure, ensuring efficient climbing and support.
• Support and Movements Notes
• Mcqs support and Movements