Introduction

The tapetum is a specialised layer of nutritive cells found between the sporogenous tissue and the anther wall within the anther of flowering plants. Tapetum is necessary for pollen grain nutrition and development, as well as a source of pollen coat precursors. The cells are often larger and feature more than one nucleus per cell. The nuclei of tapetal cells divide as sporogenous cells undergo mitosis. Because this mitosis is not always normal, many mature tapetum cells become multinucleate. Polyploidy and polyteny are also encountered on occasion. The tapetum’s exceptionally large nuclear composition aids it in delivering nutrients and regulatory chemicals to the pollen grains as they develop.

Structure of Tapetum

• Behind the epidermis and endodermis is a thick single-celled nutritive layer called the tapetum
• Their cells are diploid at first, but aberrant cell division can cause them to become polyploid
• The microsporocytes rely on them to absorb nutrients from the middle layer and deliver it to them
• Enzymes and hormones can also be secreted by tapetum cells. In the adult anther, the tapetum layer has almost vanished

Types of Tapetum 

Amoeboid Tapetum

• Alisma, Butomus, Tradescantia, Typha, and other plants have this type of tapetum, in which the tapetal cells combine to form a tapetal periplasmodium
• The pollen mother cells or developing pollen grains are surrounded by the protoplast of the fused tapetal cells as they travel into the locule
• This protoplast migration into the locule might occur during the meiotic prophase or it can be postponed until the tetrad stage
• Tradescantia tapetal cells become increasingly vacuolated during the pre-meiotic stage of sporogenous cell growth, and vesicles, possibly produced from dictyosomes, begin to be ejected from the cell
• These vesicles contain enzymes that help break down the tapetal cell wall and dissolve it quickly
• The metabolism of the tapetal cell shifts from carbohydrate production and degeneration to lipid synthesis
•  Lipid globules first develop within the plastids, then gradually protrude into the tapetal cytoplasm
• The tapetal cytoplasm becomes more vacuolated around the end of mitosis, and the second phase of polysaccharide production begins
• Finally, alterations in the anther cuticle and connective cause the tapetal cytoplasm to degrade extensively, resulting in a thin tryphine (complex mixture of hydrophilic chemicals) layer on the pollen grains’ surface at anthesis

Secretory Tapetum

• The cell wall is relatively thin, consisting of a primary wall with a low cellulose content and a middle lamella. Mitochondria, plastids, a variety of pro-Ubisch bodies, and dictyosomes are all found in the cytoplasm
• Due to the increasing amount of ribosomes and pro-Ubisch bodies, the tapetal cell wall thickens and the cytoplasm becomes denser before meiosis. On the wall facing the locule, however, thickening is uneven
• During meiosis, the number of pro-Ubisch bodies increases together with the growth of the nuclear nucleus
• The pro-Ubisch bodies are encircled by a radiating zone of ribosomes during the tetrad stage
• The pro-Ubisch entities pass through the tapetal cell membrane after separation from the tetrad and are extruded into the space between the membranes

Function of Tapetum

• Between the anther wall and the sporogenous tissue is where you’ll find it
• Tapetum is a food source for pollen grains in the early stages of development
• They also serve as a source of the pollen wall of pollen coat precursors
• It transports anthers’ nutrients
• The tapetal cells that surround the microsporocytes also generate Pollenkitt. This pollenkitt is in charge of pollen formation and nourishment
• The tapetal cells are sporopollenin’s precursors. Pollen grains have a substance called sporopollenin on their outer walls that protects them from the elements
• Ubisch bodies are ejected by Tapetum, which helps to strengthen the pollen grain membrane. The sporopollenin contains these ubisch bodies, also known as orbicules
• It also secretes the callase enzyme, which breaks down the callose molecules that hold four pollen grains together (pollen tetrad)

Conclusion

The tapetum is the anther’s lowest layer, which contains the sporogenous tissue. Microspores are produced by the sporogenous tissue, which provides enzymes and nourishment for pollen production. Due to mitotic cell division, Tapetum is generally multinucleated. Tapetum polyploidy can also be caused by abnormal cell division. Tapetum is necessary for pollen grain nutrition and development, as well as a source of pollen coat precursors. The cells are often larger and feature more than one nucleus per cell. 

The nuclei of tapetal cells divide as sporogenous cells undergo mitosis. Because this mitosis is not always normal, many mature tapetum cells become multinucleate.