Seed Development, Dormancy, and Germination Explained | Chapter 21 of Plant Physiology and Development

Seed Development, Dormancy, and Germination Explained | Chapter 21 of Plant Physiology and Development

Chapter 21 of Plant Physiology and Development examines how seeds form, enter dormancy, survive desiccation, and eventually resume growth through germination. Seeds are not just passive storage structures; they are highly regulated developmental stages that integrate genetic programs, hormonal signals, and environmental cues. This chapter traces seed development from embryogenesis through dormancy and into germination, emphasizing the roles of hormones such as abscisic acid (ABA), gibberellins (GA), and auxin. For a concise, lecture-style walkthrough of these concepts, watch the Last Minute Lecture summary below.

Watch the full chapter explanation here:

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Embryogenesis and the Structure of Seeds

Seed development begins with embryogenesis, during which a fertilized egg cell undergoes pattern formation and differentiation. The mature seed typically contains three main components:

  • Embryo – the young sporophyte, already patterned into root (radicle), shoot (plumule), and cotyledons.
  • Endosperm – a nutritive tissue that stores carbohydrates, proteins, and lipids for early seedling growth.
  • Seed coat – a protective layer derived from maternal tissues that regulates water uptake and provides mechanical protection.

Genetic programs and positional information guide the formation of these structures, while hormones such as auxin help establish polarity and tissue patterning within the developing embryo.

Hormonal Regulation of Seed Development

Three major hormones—auxin, gibberellins (GA), and abscisic acid (ABA)—play central roles in seed development and the transition into dormancy or germination.

  • Auxin contributes to embryo patterning, vascular formation, and coordination between embryo and endosperm.
  • ABA induces dormancy, promotes desiccation tolerance, and helps seeds acquire the ability to survive drying.
  • Gibberellins promote later germination by stimulating growth and enzyme production once dormancy is broken.

As the seed matures, ABA levels generally rise, reinforcing dormancy and driving the synthesis of protective proteins and sugars that stabilize cellular structures during drying.

Dormancy: Ensuring Seeds Germinate at the Right Time

Dormancy prevents seeds from germinating under unfavorable conditions and can be controlled by both physical and physiological mechanisms:

  • Physical dormancy – often due to a hard, impermeable seed coat that restricts water or gas exchange.
  • Physiological dormancy – arising from internal hormonal balances, especially high ABA relative to GA.

Environmental signals such as temperature changes, moisture availability, and light can gradually modify these constraints, either weakening the seed coat or shifting the hormonal balance to favor germination.

Environmental Cues and the Initiation of Germination

Germination begins when environmental conditions become favorable and the seed rehydrates. Key external cues include:

  • Water – imbibition reactivates metabolism and enzyme systems.
  • Temperature – controls enzyme activity and can break certain types of dormancy.
  • Light – perceived via phytochromes, particularly in small or light-sensitive seeds.

Phytochromes regulate light-dependent germination by altering GA and ABA signaling pathways and reprogramming gene expression. A shift in the GA/ABA balance toward GA promotes growth and radicle emergence.

Gibberellins, Hydrolytic Enzymes, and Nutrient Mobilization

Once germination is triggered, gibberellins play a critical role in powering early seedling growth. In cereal grains, GA produced by the embryo stimulates the surrounding aleurone layer to synthesize and secrete hydrolytic enzymes such as α-amylase.

  • α-amylase breaks down starch reserves in the endosperm into sugars.
  • Proteases and other enzymes mobilize stored proteins and lipids.

The resulting soluble nutrients are transported to the growing embryo, supporting cell division, expansion, and the emergence of the radicle and shoot.

Cotyledons, Endosperm, and Types of Germination

Seeds differ in how they store and mobilize nutrients and how seedlings emerge:

  • Cotyledon-based nutrition – in many dicots, cotyledons store reserves that are mobilized directly into the embryo.
  • Endosperm-based nutrition – in many monocots, the endosperm remains the main storage tissue and is progressively digested.

The chapter also distinguishes between epigeal and hypogeal germination:

  • Epigeal germination – cotyledons are lifted above the soil surface.
  • Hypogeal germination – cotyledons remain below ground, protected within the soil.

Seed Coat Properties, Mechanical Resistance, and Emergence

The seed coat influences both dormancy and emergence. Its thickness, permeability, and mechanical strength can:

  • Prevent premature water uptake.
  • Protect against physical damage and pathogens.
  • Impose mechanical resistance the seedling must overcome during emergence.

Stratification, scarification, or environmental weathering can alter seed coat properties and help release dormancy. Successful emergence requires coordination between embryo growth, cell wall loosening, and the mechanical constraints of soil and seed coat.

Desiccation Tolerance, Stress, and Biotechnological Applications

During late seed development, desiccation tolerance is acquired through accumulation of protective molecules and changes in cellular structure. Stress conditions such as heat, drought, or salinity can impair this process, reducing seed viability and germination success.

Biotechnological approaches aim to:

  • Improve seed longevity and storage performance.
  • Enhance germination under stress conditions.
  • Optimize hormone treatments for uniform and rapid emergence.

Understanding the hormonal, molecular, and environmental control of seed development and germination provides powerful tools for agriculture, conservation, and crop improvement.

Explore the full chapter playlist here:
Plant Physiology and Development — Complete Chapter Playlist

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⚠️ Disclaimer: These summaries are created for educational and entertainment purposes only. They provide transformative commentary and paraphrased overviews to help students understand key ideas from the referenced textbooks. Last Minute Lecture is not affiliated with, sponsored by, or endorsed by any textbook publisher or author. All textbook titles, names, and cover images—when shown—are used under nominative fair use solely for identification of the work being discussed. Some portions of the writing and narration are generated with AI-assisted tools to enhance accessibility and consistency. While every effort has been made to ensure accuracy, these materials are intended to supplement—not replace—official course readings, lectures, or professional study resources. Always refer to the original textbook and instructor guidance for complete and authoritative information.

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