Study Guide: Five Major Plant Hormones

Introduction

• Focus on five major plant hormones.
• Functions and memorization techniques for exams.

1. Auxin

Characteristics

• Growth Hormone: Causes cell elongation.
  • Accumulates in cells → elongation.
• Location: Found in growing regions (tips of leaves, shoots, buds).
• Function:
  • Promotes plant growth → shoot grows taller.
  • Phototropism: Plant turns towards light.
    • Auxin moves away from light, concentrates on shaded side.
    • Shaded side elongates more → plant bends towards light.
• Memorization Technique:
  • Visualize an ox with an elongated head ("auxin" sounds like "ox").
  • Elongated head = cell elongation, reminds of growth at tip.

2. Gibberellin

Characteristics

• Growth Hormone: Causes stem elongation.
  • Concentrated at nodes.
• Functions:
  • Stem elongation: Distance between nodes increases.
  • Affects fruit size: E.g., larger seedless grapes with gibberellin spray.
  • Crucial for seed germination.
• Memorization Technique:
  • Story of people talking gibberish to a rice plant → plant grows tall.
  • "Gibberish" relates to "Gibberellin" leading to stem elongation.

3. Cytokinin

Characteristics

• Growth Hormone: Causes cell division.
  • Responsible for new cell creation, leaf, and fruit growth.
  • Branching: Requires new cells.
• Memorization Technique:
  • "Cyto" sounds like "sight" (eyes), "kinin" sounds like "key".
  • Visualize a key entering eyes → eyes dividing into two.
  • Relates to cell division.

4. Abscisic Acid

Characteristics

• Growth Inhibitor: Prevents growth.
  • Wilting of Leaves: Historically associated with leaf drop.
  • Recent studies show it's not the primary reason for leaf drop.
• Functions:
  • Drought Response: Closes stomata to prevent water loss.
  • Seed Germination Inhibition: High levels prevent germination.
  • Ensures seeds germinate in favorable conditions (e.g., post-rain).
• Memorization Technique:
  • "Abs-cis-sick": Visualize person with great abs feeling seasick, vomiting leaves.
  • Relates to leaf drop.

5. Ethylene

Characteristics

• Function: Fruit ripening hormone.
  • Gas that breaks down cell walls, releases sugar.
  • Chain reaction: Ripe fruit emits ethylene, causing surrounding fruits to ripen.
• Memorization Technique:
  • "Eat-thai": Eating spicy Thai food → release of gas → ripens bananas.

Conclusion

• Practice visualization techniques for memorization.
• Repeated visualization helps solidify memory of hormone functions.