The tapetum is a specialised layer of nutritive cells found within the anther of flowering plants, located between the sporogenous tissue and the anther wall. Tapetum is important for the nutrition and development of pollen grains and 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 abnormal, which is why many cells of mature tapetum become multinucleated. Polyploidy and polyteny can also be seen sometimes. The tapetum's unusually large nuclear constitution helps it provide 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 pollen wall formation, transportation of nutrients to the inner side of the anther, and synthesis of callase enzyme to separate microspore tetrads.

Types of tapetum

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

locule A locule (: locules) or loculus (; : loculi) 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'' usually refers to a chamber within an ovary ...

. In contrast, the tapetal cell walls dissolve in the periplasmodial type, and their protoplasts fuse to form a multinucleate periplasmodium. 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 periplasmodium. Amongst the

monocots Monocotyledons (), commonly referred to as monocots, ( Lilianae '' sensu'' Chase & Reveal) are flowering plants whose seeds contain only one embryonic leaf, or cotyledon. A monocot taxon has been in use for several decades, but with various ranks a ...

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 oldes ...

, the first branching

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

, 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 or aquatic. Some grow in fresh water, some in marine habitats. Perhaps the most important food cro ...

, is predominantly periplasmodial. Amongst the late branching clades, the

lilioid monocots Lilioid monocots (lilioids, liliid monocots, petaloid monocots, petaloid lilioid monocots) is an informal name used for a grade (biology), grade (grouping of taxa with common characteristics) of five monocot order (biology), orders (Petrosavial ...

are nearly all secretory, while the commelinid monocots are diverse concerning the tapetal pattern.

References

Bibliography

* Plant anatomy {{Plant-morphology-stub