The term “seed” can refer to the husk, tuber, or embryo of an undeveloped plant. It can also refer to a food reserve that is enclosed in a protective outer covering. When you refer to a seed, you may be talking about anything that can be sown.
Embryos are tiny plants that have a root, stem, and one or more leaves. They are accompanied by the seed coat and endosperm, a nutritive tissue that serves as the master tissue in the young seed. Besides their functional role in a seed, embryos can provide insights into plant regeneration and totipotency.
Embryos can be cultivated artificially in the lab. These somatic embryos grow on media without the use of any plant growth regulator.
A somatic embryo is a bipolar structure that contains a number of cells, with the majority being multicellular. Its morphology is reminiscent of the zygotic embryo. However, it requires profound research to achieve true somatic embryogenesis.
Somatic embryos may be cultivated from somatic explants, leaf material, or hypocotyl. Embryos from these sources have been used to study the emergence of new varieties and to extend gene transfer area.
A seed coat is a protective covering that protects the internal parts of the seed. It also helps the seed remain viable for a long period.
Seed coats, or testas, are composed of two layers, the outer layer and the inner layer. The outer layer, called the testa, is thick and protects the seed from water and sunlight.
The inner layer, known as the integument, contains parenchyma. It provides physical protection to the seed from infection by viruses and other pests.
In the case of the angiosperms, the seed contains the embryo. The seed coat coordinates the development of the embryo and controls the dormancy of the seed.
There are many genes expressed in the seed coat tissues. Some of the genes are involved in the synthesis of flavonoid compounds.
The pericarp is the outer skin of the fruit and is composed of the outer epicarp and endocarp. It may be dry or soft and juicy. Stone fruits have a characteristic stony endocarp. In some fruit species, the pericarp is composed of a combination of stony and fleshy mesocarp.
During cellularization, the outermost part of the endosperm is transformed into aleurone cells. These cells have an axis parallel to the long axis of the grain. They are typically present in the mature seed, but may be absent in young seedlings.
The pericarp of sorghum is three-layered. An external layer corresponds to the seed coat, a middle layer is fibrous, and an inner layer contains tube cells.
The main cells of the pericarp are important channels for the rapid absorption of water. As the endosperm expands, the volume of the pericarp increases.
Endosperm is an organ that is found in most flowering plants. It plays a key role in regulating embryo growth and development. In addition to being a source of food, endosperm is also used by the plant during germination.
The structure of the endosperm is determined by plant species. In many cases, it is a mixture of oil and starch. Among the most common edible seeds are rice, wheat, and coconut. However, there are some atypical seed plants, including the Fritillaria and Lilium.
During germination, an embryo’s stem, root, and leaves develop. After the seed sprouts, it lives off of stored food. Besides providing food, the seed also contains a protective coating, the seed coat.
Most seeds contain endosperm. This tissue acts as a mechanical barrier and provides nutrients to the embryo.
Seed dormancy is a state of inactivity of seeds. It does not refer to the lack of germination but rather the slow growth of seeds, which is the result of a number of factors. The mechanisms of dormancy are largely unknown.
Dormancy occurs in seeds for many reasons, which include low water content, lack of enzymes, and the presence of growth inhibitors. Some dormancy is induced, while other is innate. For some plants, dormancy is a protective mechanism, which helps the plant survive in harsh environments.
Physical dormancy is a characteristic of higher plants. This dormancy is caused by a water-impermeable layer that prevents water and oxygen from reaching the interior of the seed. A stiffened endocarp also contributes to this type of dormancy.
Several studies have shown that seed dormancy is induced by various factors. Various treatments have been used to break dormancy, such as heat, cold, and light.