Seed Coat and Its Functions

What is the Function of Seed Coat?

A seed has three main parts.  The outer seed coat is followed by the nutritive endosperm and the internal embryo. The seed coat affects the seed germination, vigor, and longevity. Seed coat integrity affects the longevity and tolerance of the seeds to field weathering. The porosity of the seed coat determines the seed germination, especially in the case of seeds of soybeans. 

The seed coat is the external cover of a dicot seed. It is a double-layered structure that covers the growing embryo and endosperm inside. The inner layer of the seed coat is a thin-walled tegmen and the external layer is the thick-walled testa. 

Development of Seed Coat

The seed coat is developed from the integument tissues of the ovule. The integument tissues divide and grow to form thicker layers. This is the usual origin and development pattern of the seed coat. As these tissues grow and divide, they develop a thicker layer of seed coat. 

In most cases, it is developed as a result of developmental changes in the integument tissues. However, in some cases, the thickness of the seed coat depends on the original thickness of the ovule. 

Not only do the integument tissues undergo cell division but they also undergo cell differentiation to form sclereids of different kinds. In some species, the internal layers may form chlorenchyma and aerenchyma as well. The presence of sclereids makes the seed coat more rigid. 

In addition to these tissues, it also develops a water-resistant cuticle layer on the exterior. As the seed matures, the seed coat becomes drier and harder. 

What are the Functions of Seed Coat?

• The seed coat protects the seeds from external factors such as water and light.
• Most importantly, it protects the seed from water loss.
• It forms a hard and impenetrable layer against pathogens and parasites.
• Seed coat functions as a control measure that regulates seed germination by preventing germination during unfavorable conditions.
• When conditions are favorable, the seed coat promotes seed germination. This layer consists of certain light-sensitive chemicals that can trigger germination when there is enough light and water along with favorable conditions.
• The thick seed coat prevents fluctuations in the environmental conditions from affecting the embryo during its storage.

References

• Sukumaran O R. Pre-Degree Botany. Murali Publications.
• Abraham P C. Anatomy, Embryology & Microtechnique. 1999. St. Mary’s Books & Publ.
• https://doi.org/10.1590/S0100-84042001000400002

Additional Reading

• Types of Endosperm Development
• Short Note on Endosperm Haustoria