Plant Embryogenesis and Seed Development

Following fertilization, a single cell is patterned into an embryo and packaged with stored food and a protective coat to form a seed — a dormant, dispersible capsule that launches the next generation.

Definition

Plant embryogenesis is the development of the embryo from the fertilized egg through ordered cell divisions that establish the body plan, and seed development is the parallel formation of the surrounding nutritive and protective tissues into a mature seed.

Scope

This topic covers double fertilization in flowering plants, the patterning of the embryo, the formation of endosperm and the seed coat, the accumulation of storage reserves, and the establishment, maintenance, and breaking of seed dormancy in germination.

Core questions

• How does double fertilization initiate both the embryo and its food supply?
• How is the basic plant body plan established during embryogenesis?
• What controls seed dormancy and the timing of germination?

Key theories

Double fertilization

In flowering plants one sperm fertilizes the egg to form the embryo while a second fuses with central-cell nuclei to form the nutritive endosperm, coupling the embryo with its food supply.

Apical–basal patterning of the embryo

Asymmetric division of the zygote and subsequent ordered divisions, guided by auxin gradients, establish the shoot–root axis and the founding meristems of the plant.

Mechanisms

After pollination, the pollen tube delivers two sperm cells to the embryo sac; one fertilizes the egg (forming the diploid zygote) and the other fuses with the central cell to form the typically triploid endosperm. The zygote divides asymmetrically, and patterned cell divisions, organized in part by directional auxin transport, lay down the apical–basal and radial axes and the shoot and root meristems. As the seed matures it accumulates storage reserves and desiccates; the hormones abscisic acid and gibberellin balance the imposition of dormancy against its release at germination.

Clinical relevance

Seeds are the basis of agriculture and the global food supply; understanding storage-reserve accumulation, dormancy, and germination underlies seed quality, storage, breeding, and the uniform stand establishment crops require.

History

Double fertilization was discovered in flowering plants by Nawaschin and Guignard around 1898, and twentieth-century embryology and later molecular genetics in model species clarified how the embryo is patterned and how seeds mature and germinate.

Key figures

• Sergei Nawaschin
• Eduard Strasburger

Seminal works

• raven2013
• taiz2015

Frequently asked questions

What is double fertilization?

Unique to flowering plants, double fertilization is the fusion of one sperm with the egg to form the embryo and a second sperm with central-cell nuclei to form the endosperm, the tissue that nourishes the developing embryo.

Why do many seeds need a dormancy period before they germinate?

Dormancy prevents seeds from germinating immediately or under unfavorable conditions; it is broken by cues such as cold, light, or after-ripening, ensuring that germination coincides with conditions suitable for seedling survival.