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Question
Explain the role of tapetum in the formation pollen-grain wall.
Solution
Tapetum is the anther's innermost wall layer. The cells in this stratum contain big nuclei and thick cytoplasm. This layer is extremely important physiologically since it receives the majority of food from the outside. At maturity, these cells degenerate and nourish the developing microspores or pollens inside. Tapetum is the layer that secretes hormones as well as enzymes.
The major role of tapetum is to provide nutrients to pollens, but it also secretes certain extremely important chemicals such as:
- Callase enzyme: Tapetum secretes a callase enzyme, which dissolves callose compounds and joins four pollens of a pollen tetrad, thereby separating microspores or pollens of a tetrad.
- Ubisch bodies: Tapetum secretes lipid-based substances as well. Ubisch bodies are covered with sporopollenin, increasing the thickness of the exine (the outer layer of the pollen wall). Ubisch bodies are spheroidal, with a diameter of barely a few microns. These are produced exclusively by glandular tapetum.
- Pollenkitt substances: Tapetum also secretes pollenkitt, an outermost oily, thick, viscous, sticky, electron-dense homogenous covering of pollen grains in many entomophilic plants.
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