A seed is a small, hard, and nutrient-rich part of a plant. They are essential for plant reproduction and can help plants survive if they are damaged by disease or a storm.
A seed consists of three parts: the embryo, the endosperm, and the seed coat. The endosperm provides the nutrients for the new plant and contains a combination of carbohydrates, proteins and oils.
Embryonic Development
After fertilization, a zygote that forms in the ovule divides to produce new cells that grow and develop into an embryo with a root and shoot apical meristem and one to several leaves called cotyledons.
In the case of seeds, however, this development ceases and the embryo is unable to continue growing and developing unless favorable environmental conditions are met, such as nutrients or oxygen. This arresting state of seed development is referred to as arrested development.
A key question that has been raised is whether the development of fully developed embryos with environmentally cued dormancy (morphological dormancy; MD) was the ancestral state of seed plants or whether mechanisms of environmentally cued dormancy via specialized physical structures (physical dormancy; PY) or physiological responses to environmental or hormonal cues (physiological dormancy; PD) evolved after the evolution of fully developed embryos.
Endosperm Development
The endosperm is a tissue that is present in seeds of most angiosperms and provides nourishment to the embryo. In some species, the endosperm persists to the mature seed stage as a storage tissue and stores carbohydrates, proteins or lipids (e.g., castor bean, Ricinus communis).
A seed coat is a protective covering that protects the embryo and endosperm from abiotic stress and facilitates their growth and development. This coat is produced from maternal tissues and derived from the inner or outer layers of the integument.
In the developing seed, endosperm synthesis and secretion of signals contribute to the onset and control of cellularization and cell wall formation. Sulfated peptides from the endosperm regulate cuticle remodeling, increasing cuticle impermeability and promoting seedling emergence.
Germination
Germination is the initial stage of plant development, when a seed “wakes up” from its dormancy state and begins to grow. This process is initiated by a combination of factors, including air, water, and light exposure.
A seed’s inner organs remain active and perform metabolic processes such as cellular respiration while waiting for good conditions to begin growing. Some of the most important triggers for germination include air, water, and warmth.
Dormancy is a common phenomenon that inhibits the growth of a seed in conditions that would otherwise promote germination. This phenomenon is geographically and phylogenetically widespread (Baskin & Baskin, 2014).
Stratification
Stratification is the process of breaking a seed’s dormancy by subjecting it to cold or moist conditions. This helps many perennial seeds germinate during winter.
Depending on the species, some seeds require only cold stratification while others need both warm and cold. Check the seed packet for instructions.
Stratification can be performed indoors or outdoors, in a refrigerator or freezer. The cold temperatures mimic the natural conditions required to break dormancy in seeds of perennials such as native wildflowers.
Seed Dispersal
Seed dispersal is the process of moving a seed away from its parent plant to a new location, where it can germinate and grow. It is highly beneficial for the environment as it lowers competition between seeds and the parent plant, reduces overcrowding, and avoids predation.
Seeds can be moved by wind, animals, water or birds. Each type of seed has specific characteristics that determine which method will be most effective for its dispersal.
Fruit-eating animals, also known as frugivores, are the most common type of animal seed dispersers. They eat the fruit and either regurgitate or deposit the seeds in their feces.
