The tapetum is a layer of nutritive cells found within the sporangium, particularly within the anther, of flowering plants.
Tapetum is important for the development of pollen grains. 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.