The formation, dispersal and germination of seeds are crucial stages in the life cycles of gymnosperm and angiosperm plants. The unique properties of seeds, particularly their tolerance to desiccation, their mobility, and their ability to schedule their germination to coincide with times when environmental conditions are favorable to their survival as seedlings, have no doubt contributed significantly to the success of seed-bearing plants. Humans are also dependent upon seeds, which constitute the majority of the world’s staple foods (e.g., cereals and legumes), and those crops are also dependent upon seeds as propagules for establishing new fields each year. Seeds are an excellent system for studying fundamental developmental processes in plant biology, as they develop from a single fertilized zygote into an embryo and endosperm in association with the surrounding maternal tissues. As genetic and molecular approaches have become increasingly powerful tools for biological research, seeds have become an attractive system in which to study a wide array of metabolic processes and regulatory systems. The rapid pace of discovery, particularly in the model system Arabidopsis thaliana, and the complexity of the molecular interactions being uncovered provided the rationale for a book by leading experts to update our state of knowledge concerning seed development, dormancy and germination.

This volume focuses on specific aspects of seed biology associated with the role of seeds as propagules. Thus, important processes in seeds, such as the accumulation of storage reserves and their subsequent mobilization during germination, are not covered in depth here. Instead, the emphasis in the development section (Chapters 1 and 2) is on the processes that contribute to seed growth and to the induction of dormancy during maturation, rather than on the very early steps of embryogenesis, which are covered in a number of other books and reviews. Dormancy is a rather mysterious physiological state in which imbibed seeds are metabolically active, yet do not progress into germination and growth. As developmental arrest is a widespread phenomenon in biology, insight into seed dormancy will have broad implications. Chapter 3 discusses the types of dormancy exhibited by seeds and the current hypotheses concerning the mechanisms by which environmental signals are transduced into regulatory mechanisms controlling dormancy. This is followed in Chapter 4 by a discussion and examples of approaches to modeling seed dormancy and germination in an ecological context. Such models have practical utility for vegetation management in both agricultural and wildland contexts, and they also identify and quantify response mechanisms for physiological investigation.

While details are still sketchy, the genetic basis of seed dormancy is being elucidated in several systems, including Arabidopsis, rice (Oryza sativa) and other cereals. Chapter 5 provides an overview and update on the genetic regulation of seed dormancy. Genes and mutations affecting dormancy and germination have identified a number of regulatory pathways, particularly those involving gibberellins (GA) and abscisic acid (ABA), that appear to be crucial for the development, maintenance and loss of dormancy. Metabolic pathways are also involved, with lipid metabolism in particular playing an important role, as described in Chapter 6. A role for metabolic and respiratory pathways in regulating germination has been known for several decades, but new insights from work on nitric oxide discussed in Chapter 7 provide an integrating hypothesis for reinterpreting those earlier insights.

While GA and ABA are central players in regulating seed dormancy and germination, other plant hormones, including ethylene, auxin, cytokinins and brassinosteroids, play important supporting roles. The complexity of these interacting hormonal signaling networks associated with seed dormancy is discussed in Chapter 8. Feedback loops involving hormonal synthesis, catabolism and sensitivity govern diverse aspects of seed dormancy and initiation of germination. The specific genes encoding key enzymes in these hormonal synthesis and catabolism pathways are summarized in Chapter 9. The proteins involved in the signaling pathways through which these hormones act are also being uncovered. Chapter 10 reviews the important role of protein degradation pathways in controlling the transcription of germination-related genes. Once dormancy has been released and germination has been triggered, additional genes and mechanisms are involved in the growth of the embryo and its protrusion through any enclosing tissues, processes that are reviewed in Chapter 11. A final checkpoint appears to occur shortly after germination in the transition to seedling growth. Seeds are particularly sensitive to the effects of sugars at this stage, as described in Chapter 12.

Our goal in developing the book was to give a comprehensive look at seed biology from the point of view of the developmental and regulatory processes that are involved in the transition from a developing seed through dormancy and into germination and seedling growth. We wished to illustrate the the complexity of the environmental, physiological, molecular and genetic interactions that occur through the life cycle of seeds along with the concepts and approaches used to analyze seed dormancy and germination behavior. It has been over 10 years since a book devoted specifically to this topic has been published, and the progress made in that period is remarkable. The utility of Arabidopsis as a model system is evident in the focus of a number of chapters on work in this species. In addition, other chapters describe the broader implications and applications in ecological contexts of insights gained from model systems. This book provides plant developmental biologists, geneticists, plant breeders, seed biologists, graduate students, and teachers a current review of the state of knowledge on seed development, dormancy and germination and identifies the current challenges and remaining questions for future research. The book will have been a success if it contributes to stimulating a new increment of seed biology research in the next 10 years to match or exceed that of the past decade.