Integument and testa are two structures that are part of a seed’s outer protective layer. They have different origins and functions.
Key Areas Covered
What is an Integument
Integument is the outer covering of the ovule. It is made of living cells. It is very smooth and thin. Angiosperms contain two integuments, whereas gymnosperms have only one integument layer. Integument develops into a seed coat after fertilization. Generally, an integument has two layers: the inner integument and the outer integument. The inner integument is the layer that is closest to the embryo sac. It is thinner than the outer integument and develops first. The outermost integument is the layer located further from the embryo sac. It is generally thicker. Its main function is to protect the developing embryo and the endosperm inside the seed. Another function is to help control water and gas exchange during seed germination.
Integuments develop from the ovule’s primordium. Primodium is the initial structure that gives rise to the ovule. Primordium contains a group of cells that divide and differentiate to form the embryo sac as well as the integuments surrounding it.
The structure and composition of integuments vary in different species. In certain plants, integuments are thin and delicate. For example, legumes contain thinner and more delicate integuments. However, in certain other plants such as fruits and nuts, integuments are thick and hard.
After fertilization, integuments protect the developing embryo and endosperm from damage and dehydration, helping to regulate the exchange of gases and water between seeds and the external environment. It also provides nutrients to the developing embryo and endosperm.
Integuments help in the dispersal of seeds. In certain plants, integuments are adapted to be carried by water and wind. In some other plants, integuments are designed to be eaten by the animals.
What is Testa
Testa is the outer covering of the seed. It is also known as the seed coat. The main function of the testa is to act as a protective layer that helps in the prevention of damage to the embryo and the endosperm. The structure and the composition of testa can vary depending on the plant species and composition.
Testa is made of two layers. The outer layer is the exotesta, while the inner layer is the endotesta. The exotesta is usually thicker and harder than the endotesta. It is composed of several layers of cells that contain high amounts of lignin. The endotesta is thinner and more delicate than the exotesta. The endotesta is single-cell layered. The cells of the testa are nonliving and thick and hard.
Testa protects the seed from mechanical damage, pests, and pathogens. It also helps to regulate the exchange of gases and water between the seeds and the external environment. Furthermore, testa has an impact on the nutritional content and the flavour of the seeds. In addition, it has an impact on seed dormancy and germination. Testa also plays a role in seed dispersal. In certain cases, seeds are adapted to be carried by water and wind, whereas other seeds have hooks and barbs that help them to attach to other substances.
Difference Between Integument and Testa
Integument is the outer covering of the ovule, whereas testa is the outer covering of the seed.
Nature of Cells
The cells of the integumet are thin and smooth, whereas the cells of the testa are thick and hard. In addition, integumet contains living cells, whereas testa contains nonliving cells.
Integument protects the ovule, whereas testa protects the developing embryo.
While integuments have no role in seed dormancy, testa have an impact on dormancy and germination.
Integument consists of two parts as inner integument and outer integument, while testa has two parts as exotesta and endotesta.
Integuments and testa are two structures that are a part of the seed’s outer protective layer. The main difference between integument and testa is that integument is the outer covering of the ovule, whereas testa is the outer covering of the seed.
1. Debeaujon, I et al. “Influence of the testa on seed dormancy, germination, and longevity in Arabidopsis.” Plant physiology vol. 122,2 (2000).
2. “Integument.” NYBG. Steere Herbarium.
1. “Ovules diagram” By BlueRidgeKitties (CC BY 2.0) via Flickr
2. “Picea sitchensis seedling. Seed testa being released. Sitka Spruce” By Rosser1954 – Own work (CC BY-SA 4.0) via Commons Wikimedia