Tapetum – Types and Functions

The functions of tapetum entail the supply of nutrition and enzymes essential for the process of microsporogenesis and the successive development of pollen grains. This article discusses how the tapetum contributes significantly to the reproductive success of flowering plants, its types, and the functions it performs.

What is Tapetum?

The tapetum is the innermost protective layer that surrounds the pollen-developing mother cells (microspores) present within the anther. Inside the anther, the tapetum is positioned as a uniform layer around the sporogenous tissue. This specialized layer acts as a medium for transferring nutrients from the middle layer to the sporogenous tissues which in turn is responsible for pollen grain formation.

Structure of Tapetum

The tapetum is a single celled nutritive layer found behind the epidermis and endodermis. intially the cells are diploid but after several cell divisions they become polyploid. the cells are known as tapetal cells that have dense cytoplasm and a prominent nuclei. The cells are large because they provide nutrition for the developing pollen grains. Spherical cells called Pro-ubisch are present in the cells that help in the thickening of the exine.

In plants that engage in sexual reproduction involving two separate gametes- male and female, the tapetum aids this process by supporting the development of male gametes, especially pollen grains, within the anther.

The tapetum ensures that the pollen grains mature adequately, so as to obtain the reproductive success of flowering plants.

Types of Tapetum

Based on developmental characteristics and functions, tapetum can be categorized into different types. Some of these types are discussed below:

1. Secretory Tapetum: This kind of tapetum produces and secretes enzymes and nutrients, important for the formation and maturation of pollen grains.
2. Plasmodial Tapetum: In this type, the cells of tapetum undergo several rounds of nuclear division without cytokinesis (division of cytoplasm), resulting in a multinucleate mass of cytoplasm called a plasmodium. This plasmodium’s primary function is to provide nourishment to the developing pollen grains.
3. Glandular Tapetum: This type of tapetum secretes various substances that aid in the formation, nourishment, and maturation of pollen grains.
4. Amoeboid or Plasmodial Tapetum– In this type, the cells of tapetum undergo several rounds of nuclear division without cytokinesis (division of cytoplasm), resulting in a multinucleate mass of cytoplasm called a plasmodium. This plasmodium’s primary function is to provide nourishment to the developing pollen grains.
5. Amitotic Tapetum: In this type, the cells of the tapetum do not undergo mitotic divisions but provide essential nutrients and metabolites directly to the developing pollen grains.
6. Binucleate Tapetum: In this type, the cells of the tapetum consist of two distinct nuclei, performing functions specific to the formation and maturation of pollen grains.

Functions of Tapetum

The functions of tapetum are characterized by its role in providing nourishment to the developing pollen grains, supplying vital nutrients and enzymes for microsporogenesis (formation of microspores within the anthers of flowering plants), promoting pollen maturation, and guaranteeing reproductive success in flowering plants.

Nutrition and Support for Pollen Development

One of the primary functions the tapetum performs is the supply of essential nutrients and metabolic support to the developing pollen grains. As the pollen grains mature, the tapetum provides proteins, lipids, and other necessary substances to the pollen grains, to aid their maturation.

Degradation and Release of Pollen

During the maturation process, the tapetum undergoes apoptosis (programmed cell death) and releases the necessary enzymes that assist in the degradation of its cellular organelles. This degradation process helps in the formation of the pollen’s outer layer, also known as exine, and assists in the release of mature pollen grains from the anther.

Protection of Developing Pollen

The tapetum provides a protective environment for properly developing the pollen grains by shielding them from external stresses and strains. By forming a uniform layer around microspores (precursors to pollen grains), the tapetum helps maintain optimal conditions for pollen maturation within the anther.

Synthesis of Sporopollenin

The tapetum plays an essential role in the synthesis and deposition of sporopollenin, a biological heteropolymer that forms the exine (outer layer) of pollen grains. Sporopollenin provides structural support and protection to pollen grains, allowing them to resist various environmental challenges during dispersal and fertilization.

Conclusion

The tapetum is a crucial layer within the anther of flowering plants, performing functions vital for the successful reproduction in plants. Its multiple roles include nourishing and supporting developing pollen grains, supplying nutrients for microsporogenesis, and helping pollen mature. Additionally, the tapetum facilitates protection against external stresses, aids the synthesis of sporopollenin—a key component of pollen grain structure—and coordinates the timely degradation and release of mature pollen. Ultimately, the tapetum’s complex mechanisms emphasize its vital contribution to the reproductive success of flowering plants.

FAQs on Functions of Tapetum

1. What is the Function of Sporopollenin?

Sporopollenin is a highly resistant biopolymer that forms the outer layer, known as exine, of spores and pollen grains in plants. The primary function of sporopollenin is to provide structural support and protection to spores and pollen grains.

2. Are there different Types of Tapetum?

Yes, tapetum based on developmental characteristics and functions can be categorized into various types, such as secretory tapetum, glandular tapetum, amitotic tapetum, plasmodial tapetum, and binucleate tapetum.

3. Why is the Tapetum essential for Reproductive success in Plants?

The tapetum plays a fundamental role in the proper development, nourishment, and maturation of pollen grains. These three processes are essential for the reproductive success of flowering plants.

4. What happens to Tapetum cells after supporting Pollen development?

After pollen development, tapetum cells undergo programmed cell death (apoptosis), secreting enzymes that facilitate the maturation and release of mature pollen grains from the anther.

5. What happens if the Tapetum does not function properly?

If the tapetum does not function properly, it can lead to male sterility in plants, affecting pollen development, fertilization, and seed production, thereby impacting crop yields.