Whether you are growing your own vegetables or flowers, seeds are a great way to get a head start. They contain all of the starting materials necessary to produce a healthy and nutritious plant.
Seeds serve a variety of functions in plants, including nourishment of the embryo, dispersal, and dormancy during unfavorable conditions. Understanding the biology behind seeds will help you choose the best seeds for your garden.
What is a seed?
Seeds are the way certain plants reproduce. They have an embryo and a protective covering called the seed coat. They are produced in both angiosperms (flowering plants) and gymnosperms (conifers and ginkgoes).
Angiosperm seeds are produced in a hard or fleshy structure called a fruit that encloses the seeds for protection in order to secure healthy growth. In gymnosperms, the seeds begin development “naked” on the bracts of cones.
Seeds contain a source of stored food for the developing embryo, called endosperm. This food storage tissue is usually triploid, and is rich in oil or starch and protein.
How do seeds grow?
Seeds are tiny, but they contain everything a plant needs to grow into a new one. That includes water, the right temperature and a whole bunch of food for the embryo that grows inside.
When a seed is planted it begins to send out roots that search for water. Once the seed has a root it can absorb more water to help it grow bigger and stronger.
Once the seed has a root it starts to get bigger and produce enzymes that ramp up the metabolism of the embryo, breaking down the food stored in the endosperm for energy. This helps the small plant begin photosynthesis, or turning light into food for itself.
Eventually, the radicle (first root) and then the shoot start to emerge from the seed. These are the two parts that will grow into leaves, and start the process of photosynthesis again. Watching seeds sprout is a great way to learn about how plants grow!
How do seeds germinate?
The germination process is the beginning of plant growth from a seed. It involves a series of steps that are triggered by environmental factors such as water, temperature, light exposure, and oxygen availability.
First, the dry seed takes up water. This results in swelling of the seed and a rupture of its seed coat. Then, a root grows downwards to access underground water and a shoot grows upwards towards sunlight.
Step 1: The uptake of water triggers a series of enzymes that initiate growth. These include the formation of the radicle (primary root) and plumule (shoot), and cotyledons, which unfold to begin photosynthesis.
The optimum water level is critical for the seed to germinate. Too much water inhibits germination, while too little water stops it. Temperature is also an important factor, with some seeds requiring cool winter temperatures to break dormancy. Others need to experience alternations between warm and cool conditions. Oxygen is also important, as germinating seeds respire vigorously to release energy for their growth.
How do seeds grow into plants?
Seeds need water, the right temperature and a bit of light to grow into plants. But there’s a lot more to it than that, and some seeds have requirements that are quite strange!
First of all, they need to survive a long period of dormancy. Dormancy is a time when a seed’s cells remain active but don’t release energy for growth.
The next step is called germination. This involves the reactivation of the metabolic pathways that lead to plant growth and the emergence of the radicle or seed root and plumule or shoot.
Most seeds are surrounded by a protective covering called the seed coat. The seed coat helps the seed survive long periods of heat, drought and cold. It also protects the embryo from microorganisms that destroy the seed.
