The tapetum is a specialised layer of nutritive cells found within the anther, of flowering plants, where it is located between the sporangenous tissue and the anther wall. Tapetum is important for the nutrition and development of pollen grains, as well as a source of precursors for the pollen coat.P.L. Polowick, V.K. Sawhney 1993
Differentiation of the Tapetum During Microsporogenesis in Tomato (Lycopersicon esculentum Mill.), with Special Reference to the Tapetal Cell Wall
Annals of Botany, Volume 72, Issue 6, December 1993, Pages 595–605 The cells are usually bigger and normally have more than one nucleus per cell. As the sporogenous cells undergo mitosis, the nuclei of tapetal cells also divide. Sometimes, this mitosis is not normal due to which many cells of mature tapetum become

multinucleate Multinucleate cells (also known as multinucleated or polynuclear cells) are eukaryotic cells that have more than one nucleus per cell, i.e., multiple nuclei share one common cytoplasm. Mitosis in multinucleate cells can occur either in a coordinat ...

. Sometimes polyploidy and polyteny can also be seen. The unusually large nuclear constitution of the tapetum helps it in providing nutrients and regulatory molecules to the forming pollen grains. The following processes are responsible for this: * Endomitosis * Normal mitosis not followed by cytokinesis * Formation of restitution nuclei * Endoreduplication Tapetum helps in pollenwall formation, transportation of nutrients to inner side of anther, synthesis of callase enzyme for separation of microspore tetrads.

Types of tapetum

Two main tapetum types are recognised, secretory (glandular) and plasmodial (amoeboid). In the secretory type a layer of tapetal cells remains around the anther

locule A locule (plural locules) or loculus (plural loculi) (meaning "little place" in Latin) is a small cavity or compartment within an organ or part of an organism (animal, plant, or fungus). In angiosperms (flowering plants), the term ''locule'' usu ...

, while in the plasmodial type the tapetal cell walls dissolve and their

protoplasts Protoplast (), is a biology, biological term coined by Johannes von Hanstein, Hanstein in 1880 to refer to the entire cell, excluding the cell wall. Protoplasts can be generated by stripping the cell wall from plant, bacterium, bacterial, or fu ...

fuse to form a multinucleate plasmodium. A third, less common type, the invasive non-syncytial tapetum has been described in '' Canna'', where the tapetal cell walls break down to invade the anther locule but do not fuse to form a plasmodium. Amongst the

monocots Monocotyledons (), commonly referred to as monocots, ( Lilianae '' sensu'' Chase & Reveal) are grass and grass-like flowering plants (angiosperms), the seeds of which typically contain only one embryonic leaf, or cotyledon. They constitute one of ...

Acorales ''Acorus'' is a genus of monocot flowering plants. This genus was once placed within the family Araceae (aroids), but more recent classifications place it in its own family Acoraceae and order Acorales, of which it is the sole genus of the old ...

, the first branching

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

has a secretory tapetum, while the other alismatid clade,

Alismatales The Alismatales (alismatids) are an order of flowering plants including about 4,500 species. Plants assigned to this order are mostly Tropical vegetation, tropical or Aquatic plant, aquatic. Some grow in fresh water, some in marine habitats. ...

are predominantly plasmodial. Amongst the late branching clades, the lilioid monocots are nearly all secretory while the commelinid monocots are diverse with respect to tapetal pattern.

References

Bibliography

* Plant anatomy {{botany-stub