Lecture Notes: Control and Coordination in Plants

Lecture Overview

• Discussion on the different ways plants perceive their environment and react accordingly, similar to how human bodies function but through different mechanisms like movement.
• Classification of plant movements into nastic and tropic movements.

Plant Movements

Nastic Movements (Nasty Movements)

• Definition: Non-directional movements that occur in response to stimuli, not dependent on growth.
• **Characteristics: ** These movements are temporary and reversible.
• **Examples: **
  • Thigmonasty (Touch-induced): Movement of sensitive plant leaves (Mimosa pudica) when touched.
  • Photonasty (Light-induced): Opening and closing of certain flower petals based on light availability.
  • Thermonasty (Temperature-induced): Petal movements in response to temperature changes.
• **Key Points: **
  • Nastic movements are usually immediate and involve movement but not growth.
  • Commonly observed in leaves and flowers.

Tropic Movements (Tropisms)

• Definition: Directional growth movements in response to external stimuli.
• Characteristics: These movements have a specific direction (towards or away from the stimulus) and involve growth.
• **Types of Tropic Movements: **

  1. Phototropism (Light):

     • Positive Phototropism: Growth towards the light (e.g., shoot growth towards light).
     • Negative Phototropism: Growth away from light (less common).

  2. Gravitropism (Gravity):

     • Positive Gravitropism: Growth towards gravity (e.g., root growth downward).
     • Negative Gravitropism: Growth away from gravity (e.g., shoot growth upwards).

  3. Hydrotropism (Water):

     • Growth towards water (e.g., root growth towards a water source).

  4. Thigmotropism (Touch):

     • Growth towards mechanical support (e.g., tendrils of climbing plants wrapping around a support).

  5. Chemotropism (Chemicals):

     • Growth in response to chemicals (e.g., pollen tube growth towards the ovule).

Plant Hormones

Growth Promoting Hormones

1. Auxins:

   • Promotes elongation of cells in shoots and is involved in phototropism and gravitropism.
   • Delays the aging of leaves and fruits.

2. Gibberellins:

   • Stimulate stem elongation, seed germination, and flowering.

3. Cytokinins:

   • Promote cell division and delay the aging of leaves.

Growth Inhibiting Hormone

1. Abscisic Acid (ABA):
   • Induces closure of stomata during water stress.
   • Promotes dormancy in seeds and buds.
   • Inhibits growth-promoting activities.

Fruit Ripening Hormone

1. Ethene (Ethylene):
   • Promotes fruit ripening and leaf abscission.
   • Induces aging in plants.

Feedback Mechanism in Plants

• Plants regulate the timing and amount of hormone release through feedback mechanisms.
• These mechanisms are necessary to maintain homeostasis within the plant system.

Summary

• Plants can sense and respond to stimuli in their environment through movements and hormonal coordination.
• Movements can be nastic (growth-independent) or tropic (growth-dependent).
• Plant hormones play a crucial role in coordinating various functions such as growth, development, and stress responses.

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Always remember, similar to humans, plants too have intricate systems coordinating their growth and response to their environment!

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