What is Tapetum?
In the anther of flowering plants, tapetum is a specialised layer of nutritive cells situated between the sporogenous tissue and the anther wall. The anther is the part of the stamen where pollen is produced. Tapetum is a source of precursors for the pollen coat and is crucial for the nourishment and growth of pollen grains. It constructs the pollen sac's innermost layer and provides the pollen grain's surface with a lipid coating. It is an anther's diploid tissue. In the following sections, we will study the structure of the tapetum and its different functions.
What is a Tapetum?
Tapetum is the anther's innermost cell layer surrounding developing pollen mother cells (PMCs) and/or microspores, supplying nutrition and enzymes needed for microsporogenesis and pollen maturation. Two separate sexes engage in sexual reproduction in plants. Gametes are the blooming plant's reproductive cells. The flower reproduces sexually since there are both male and female gametes. The male gamete pollen grains develop in the anther and pollen sac in which pollen grains are generated. The epidermis, endothecium, middle layer, and tapetum are the four layers that surround each pollen sac.
The tapetum is the innermost layer, while the epidermis is the outer layer. The tapetum is present as a uniform layer surrounding the sporogenous tissue. The tapetum passes the food from the middle layer to sporogenous tissues. These sporogenous tissues form pollen grains and get nutrition from tapetum.
The Anther Lobe
Tapetal Cells
The cells that are present in the tapetum layer are known as tapetal cells. The tapetal cells may be uni-, bi-, or multinucleated. The tapetal cells have dense cytoplasm and conspicuous nuclei. These cells are large because they have to provide nutrients to develop pollen grains inside the pollen sac. These tapetal cells store food for developing pollen grains. Pro-ubisch is spherical bodies that are present in these tapetal cells. These pro-ubisch bodies are helpful for exine thickening.
Types of Tapetum
Tapetum is divided based on their behaviour, such as amoeboid (plasmodial) tapetum and secretory (glandular) tapetum.
Amoeboid Tapetum
In the amoeboid tapetum, the tapetal cells grow and fuse with each other. Their protoplasts fuse but not their nuclei. So it is a multinucleated layer. Then these cells form a plasmodium-like structure and move between MMC and provide nutrition. As pollen grains mature and the anther lobe dehisces, these plasmodia become dehydrated due to absorption of pollen grains and deposit as debris on the wall of pollen grains and help form some parts of exine (outer layer of pollen grains).
Alisma orientale, lily(Lilium), and Typha latifolia have these types of tapetum.
Secretory Tapetum
These tapeta remain in their original shape till the maturation of pollen grains. They are intact with the middle layer and do not change their shape throughout the development of pollen grains. These cells fuse just after the formation of the tapetum and remain multinucleated at the end of the maturation of the pollen grain. Tapetal cells become thick-walled and increase their number of pro-ubisch bodies just before the microspore mother cells (MMC) undergo the meiosis process. The ubisch bodies are only produced by tapetum and help in the exine formation.
The cells in this layer secrete their secretions slowly, so-called secretory tapetum, and help in the exine formation. In angiosperms, it is the most common type of tapetum. Helleborus foetidus and Nigella damascena are some species that have these types of tapetum.
Tapetum Brain
The corpus callosum, a nerve tract under the cerebral cortex of the brain, is present in placental animals, and the tapetum is a component of this framework. To improve night vision, the choroid's tapetum lucidum, a reflective region, bounces light back into the retina. The tapetum lucidum is a reflecting region of the choroid layer that is pigment-free. Choroid coat is another name for it.
Are Tapetal Cells Haploid or Diploid?
The innermost layer full of nutritive cells within the anther acts as a harbinger of sporopollenin, which is a chemical that protects pollen from external adverse conditions. Tapetal cells go through endomitosis, where the nucleus and nuclear membrane splits, but cytokinesis doesn’t happen, so they become multinucleated, having more than one nucleus per cell.
The tapetal cells are metabolically active as their division happens through endomitosis, and they contain dense cytoplasm thus, they are polyploidy, which happens when a cell possesses one or more additional sets of chromosomes. In this, mitosis normally happens till cytokinesis doesn’t happen. Two sets of chromosomes are thus constituted into a common nuclear membrane forming a restitution nucleus. So, tapetal cells are polyploid.
Function of Tapetum
The tapetum provides various enzymes, hormones, amino acids, and nutritive materials to microsporocytes during the development of pollen grains. Tapetal cells of tapetum store the food in the early stage of microsporogenesis. It transfers food from the middle layer to the spore mother cells. It produces ubisch bodies coated with sporopollenin to cause thickening of the exine. It secretes an oily material that forms a pollenkitt of mature pollen grains. It adds some proteins to the exine that help in compatibility with stigma.
Interesting Fact
A salient process tapetum acts out is the secretion of callose enzyme, which sub-divides the callose compounds used to form four pollen (pollen tetrad).
Important Questions
Is tapetum dependent on male meiosis for progression in plants? Ans: In higher plants, male meiosis is an important process during microsporogenesis and is vital for male fertility and seed set. Meiosis involves the organising of chromosomes and cytoskeleton, which takes place in sexual cells. In the normal development of the tapetum, the somatic layer surrounding male meiosis is important for completing the cycle. Disruptions in tapetum development cause changes in the range of genes involved in male reproduction.
What is the role of pollen in the protection of male sperm from harsh conditions?
Ans: The pollen acts as a biological protector of the male sperm from harsh conditions as it's covered by a cell wall made of exine, whose major constituent is sporopollenin. Tapetum is in close contact with the developing gametophytes and acts well in pollen coat and pollen wall formation. Evidence indicates that sporopollenin is built through catalytic enzyme reactions in the tapetum.
Key Features
Tapetum is vital for the growth and development of pollen grains.
Tapetum is the specialised innermost layer found within the anther of flowering plants.
The radically large nucleus of the tapetum helps in the storage of the necessary nutrients.
Types of tapetum include secretory and plasmodium.
Conclusion
The tapetum is the innermost layer of the anther wall and covers the sporogenous tissue. It is a layer that stores food and provides for developing microspore mother cells. This is a diploid tissue of the male part of the plants. The above information helps to understand the concept of the tapetum layer of the anther wall in angiosperms.
FAQs on Tapetum
1. What is the tapetum in a plant and where is it located?
The tapetum is the innermost nutritive layer of cells in the anther wall of a flowering plant. It is located just inside the middle layers and directly surrounds the sporogenous tissue, which contains the developing pollen mother cells (PMCs) or microspores. Its primary role is to provide nourishment for their development.
2. What are the main functions of the tapetum in flowering plants?
The tapetum performs several critical functions for pollen development, as per the CBSE syllabus for the 2025-26 session. Its main roles include:
- Nourishment: It provides essential nutrients to the developing microspores.
- Enzyme Secretion: It secretes the enzyme callase, which dissolves the callose wall enclosing the pollen tetrad, releasing the individual microspores.
- Pollen Wall Formation: It contributes significantly to the formation of the exine (outer pollen wall) by secreting sporopollenin precursors, which are polymerised on structures called Ubisch bodies.
- Pollenkitt Synthesis: It produces an oily substance called pollenkitt, which forms a sticky layer on the surface of pollen grains in insect-pollinated plants, aiding in pollination.
3. How do the secretory (glandular) and amoeboid (plasmodial) types of tapetum differ?
The two main types of tapetum differ in their structure and method of providing nutrition. The secretory tapetum remains intact in its cellular position throughout pollen development, secreting nutrients into the anther locule. In contrast, the amoeboid tapetum breaks down its cell walls early, and its protoplasts fuse to form a multinucleate mass called a plasmodium, which moves in among the developing microspores to nourish them directly.
4. Why do tapetal cells often become multinucleated or polyploid?
Tapetal cells become multinucleated (having more than one nucleus) or polyploid (having multiple sets of chromosomes) to support their high metabolic activity. This process, often involving endomitosis (nuclear division without cell division), allows the cells to produce and store large amounts of nutrients, enzymes, and hormones required for the rapid development of numerous pollen grains. An enlarged nuclear content enhances the cell's synthetic capabilities.
5. What is the specific role of the tapetum in forming sporopollenin?
The tapetum does not synthesise sporopollenin directly but plays a crucial role in its formation on the pollen wall. Tapetal cells produce and secrete precursor substances (pro-Ubisch bodies) into the anther cavity. These precursors are then polymerised to form sporopollenin, one of the most resistant organic materials known, creating the tough and protective outer layer (exine) of the pollen grain.
6. Is the tapetum found in the human brain or eye?
No, the tapetum discussed in plant biology is not found in humans. There is a confusion with a similarly named structure, the tapetum lucidum, which is a reflective layer found in the eyes of many nocturnal animals that helps with night vision. This is completely different from the plant tapetum found in the anther. There is also a structure called the tapetum of the corpus callosum in the human brain, which is a layer of fibres, but it is unrelated to the nutritive function of the plant tapetum.
7. What would happen to pollen grain development if the tapetum degenerated prematurely?
If the tapetum degenerated too early, it would lead to male sterility. The developing microspores would be starved of essential nutrients, enzymes, and the precursors for wall formation. This would result in the formation of non-viable, aborted, or empty pollen grains that are incapable of successful germination and fertilisation, highlighting the tapetum's indispensable role in sexual reproduction in plants.
