Lecture Notes: Plant Responses to Signals

Introduction

• Sunflowers: Track sun across the sky, pivot back to face east overnight. Demonstrates plants' responsiveness.
• Chapter Focus: "Plant responses to internal and external signals."
• Objective: Explore how plants navigate their environment using signals.

Signal Transduction Pathways

• Purpose: Convert external environmental cues into internal actions.
• Process: Reception, Transduction, Response.
  • Reception: Specific receptor protein detects stimulus (e.g., light).
  • Transduction: Signal is relayed and amplified through relay proteins and second messengers (e.g., calcium ions, cGMP).
  • Response: Changes occur via transcriptional regulation or post-translational modification.

Plant Hormones

• Role: Chemical messengers influencing plant behavior.
• Types:
  • Auxin: Stimulates stem elongation, root growth, phototropism, gravitropism, apical dominance.
  • Cytokinins: Promote cell division, anti-aging effects, counteract auxin in apical dominance.
  • Gibberellins: Stimulate stem elongation, seed germination, fruit development.
  • Abscisic Acid (ABA): Growth inhibitor, stress response, seed dormancy.
  • Ethylene: Ripens fruit, stress response, triple response in seedlings.
  • Brassinosteroids: Promote cell expansion, seed germination.
  • Jasmonates: Defense roles, various developmental processes.
  • Strigolactones: Branching control, attract beneficial fungi, parasitic weed germination.

Light and Photomorphogenesis

• Importance: Light is crucial for photosynthesis and development.
• Photoreceptors:
  • Blue Light Photoreceptors: Cryptochromes and Phototropin, involved in phototropism, stomatal opening.
  • Phytochromes: Detect red and far-red light, involved in seed germination, shade avoidance.
• Biological Clocks: Plants have circadian rhythms for processes like stomatal opening.

Conclusion

• Plants have complex communication and response systems using signals and hormones.
• Understanding these processes reveals the dynamic nature of plant life.
• Practical applications in agriculture and horticulture.