AGR 3301 Lesson 2: Seed Germination and Dormancy

Lesson 2 Seeds Germination and Dormancy 4APRIL2026.pdf

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Explore the foundational physiological processes of Seed Germination and Dormancy in this comprehensive lesson from the AGR3301 Crop Physiology course at Universiti Putra Malaysia (UPM). This module transitions from growth analysis to the critical start of the plant life cycle, focusing on how internal mechanisms and environmental factors determine successful crop establishment.

📌 What is this lecture about?

This lecture introduces the fundamental concepts of seed biology, focusing on how seeds remain dormant and what triggers them to germinate. It explains how seeds function as living systems, how they survive under unfavorable conditions, and how they eventually develop into independent seedlings.

🌾 Key Topics Covered

1. 🌱 Nature of Seeds

Seeds are living structures formed through sexual reproduction. Each seed contains:

• An embryo (young plant)

• Food reserves (for early growth)

• A seed coat (protection)

Despite appearing inactive, seeds are alive and continuously respire at a slow rate.

2. 🌍 Seed Diversity and Survival

Seeds vary greatly in:

• Size (from tiny orchid seeds to large coco-de-mer)

• Adaptations for survival and dispersal

This diversity allows seeds to survive in different environments until conditions are suitable for growth.

3. 🛑 Seed Dormancy

Dormancy is a condition where a viable seed fails to germinate even under favorable conditions.

Causes of dormancy include:

• Hard seed coat (physical barrier)

• Chemical inhibitors (e.g., ABA)

• Immature embryo

Breaking dormancy can occur through:

• Scarification (breaking seed coat)

• Environmental signals (light, temperature, water)

• Biological activity (microbes, enzymes)

4. 🌿 Germination Process

Germination occurs in three main stages:

Pre-germination

• Water uptake (imbibition)

• Activation of metabolism and enzymes

Germination

• Seed coat breaks

• Radicle (root) emerges first

Post-germination

• Root and shoot develop

• Seedling begins independent growth

5. ⚙️ Mobilisation of Food Reserves

Stored nutrients (starch, proteins, lipids) are broken down into usable forms:

• Starch → sugars

• Proteins → amino acids

• Lipids → fatty acids & glycerol

This process is regulated by plant hormones:

• Gibberellin (GA) → promotes germination

• Abscisic acid (ABA) → inhibits germination

6. 🌞 Seedling Establishment

After germination:

• Roots grow downward

• Shoots grow upward and reach light

• Photosynthesis begins

• Seed becomes independent from stored reserves

7. 🌱 Types of Germination

• Epigeal germination – cotyledons emerge above ground

• Hypogeal germination – cotyledons remain below ground

✅ Conclusion

Seeds are living but dormant systems that require the right conditions: water, oxygen, and temperature—to germinate. Successful germination leads to the formation of a seedling capable of independent growth.