What is "tapetum"

Tapetum \Ta*pe"tum\, n. [NL., from L. tapete a carpet, a tapestry.] (Anat.) An area in the pigmented layer of the choroid coat of the eye in many animals, which has an iridescent or metallic luster and helps to make the eye visible in the dark. Sometimes applied to the whole layer of pigmented epithelium of the choroid.

of the eye, 1713, from Medieval Latin tapetum, from Latin tapete, collateral form of tapes "carpet, heavy cloth with inwrought figures" (see tapestry).

n. (context anatomy English) A membranous layer of tissue

Tapetum (Latin for carpet or tapestry) can refer to:

• Tapetum (botany), tissue within the sporangium (especially the anther), which provides nutrition for growing spores
• Tapetum lucidum, a reflective tissue layer associated with the retina of some vertebrates
• Tapetum of corpus callosum, a section of the brain

The tapetum is a specialised layer of nutritive cells found within the sporangium, particularly 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. 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. 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.