In botany, a seed is the characteristic reproductive body of flowering plants (angiosperms) and gymnosperms. It contains a miniature undeveloped plant (the embryo) and stored food reserves, enclosed within a protective coat.
Most seeds “wake up” and grow into new plants when they are exposed to conditions favorable for germination. Such conditions include:
A seed develops as a package inside which is an embryo and stored food. Its outside coating, known as the seed coat, forms from sporophyte tissues of its parent plant.
Embryonic development of seeds is complex. A specialized region of the outer layer, called the ectoderm, gives rise to the skin and nervous system. A groove in the center of the embryo encloses the neural tube, which will eventually become the brain and spinal cord. Tissues at the edges of this groove migrate throughout the embryo and give rise to peripheral nervous system (PNS) structures as well as non-nervous tissue.
A key feature of seed plants is that they undergo double fertilization during embryogenesis. This results in a food reserve, or endosperm, which feeds the embryo during germination. This feature differs from gymnosperms, such as conifers, which have no endosperm. During the germination process, an embryo grows down through the hypocotyl and epicotyle into the cotyledons or seed leaves of a monocot or dicot plant.
Seeds contain the starting materials for complex plants, and as such are dense in nutrients. They are high in protein, healthy fats and dietary fibre as well as vitamins, minerals and antioxidants. They support optimal immune, hormonal and cardiovascular health.
Seeds are also a great source of plant lignans, which help reduce the risk of heart disease and certain cancers. They can be eaten whole or ground into a powder to add to your favourite foods.
Often overlooked for their more glamorous cousins nuts, seeds are packed with powerful nutrients and deserve to be included in everyone’s diet. They are a good source of protein, healthy fats and dietary fibre for omnivores, paleo and low FODMAP diets. They are also a good source of vitamin E and folate.
Seeds undergo a period of dormancy in order to survive in harsh conditions. The depth of the dormancy is determined by morphological and physiological properties. Marianna Nikolaeva developed a dormancy classification system which includes five classes; physiological (PD), morphological dormancy (MD), physical dormancy (PY) and combinational dormancy (PY + PD).
Physiological dormancy is induced by hormonal interactions between abscisic acid and gibberellins. Physical seed dormancy is mainly caused by water-impermeable seed or fruit coats and by phenolic compounds that inhibit germination. This type of dormancy is phylogenetically restricted and is probably an adaptation to specialized life strategies or habitats.
The germination of seeds is dependent on the balance between genetic and environmental factors that control this process. Genetically manipulated seeds can be used to identify the genes that promote or reduce germination. However, these mutants have pleiotropic effects on other processes which makes it difficult to distinguish the specific role of individual genes. Ongoing studies should allow a better insight into the regulation of these genes.
Getting the seeds to another place away from the parent plant is a crucial step. Seeds and fruits employ a variety of strategies to disperse themselves.
Many fruit-producing plants rely on animals to hitch a ride on the backs of their seeds. Animals, referred to as frugivores, are attracted by the attractive colors and scents of a plant’s fruits. They then eat them and either pass the seeds through their digestive tracts or drop them somewhere else (depending on the behavior of the animal).
Some plants produce fruits that float in water. When water currents carry the seeds, they may be transported far distances to new locations where they are able to grow. Water lilies are an example of this type of dispersal. Likewise, the seeds of the coco de mer palm tree float, allowing them to travel between remote islands in the Indian Ocean. Some seeds have hooks or barbs, which allow them to attach themselves to animals’ fur or feathers. If you’ve ever been on a hike and found a seed stuck to your coat, this is an example of animal-aided seed dispersal.