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Note:
- Normally each microspore mother cell can form tetrad by meiotic division. But in some plant like Zostera, some microspore mother cells become sterile and provide nutrition to rest of microspore mother cells.
- Similarly, tapetum is not well developed in Gentianaceae family so some cells of sporogenous tissue become sterile and provide nutrition to remaining sporogenous cells.
The arrangement of the microspores in tetrad condition as follows:Different types of Microspores
(i) Tetrahedral tetrad: Four haploid microspores arranged in tetrahedral form.
Example: Dicotyledons - (Capsella).
Tetrahedral Tetrad(ii) Isobilateral tetrad: This condition is found in monocotyledons. Microspores are arranged at the lateral side of each other.
(iii) Decussate Tetrad: In this, two microspores lies at the right angle of other microspores.
Example: Magnolia
(iv) T-Shaped tetrad: Two microspores lie longitudinally and two microspores lie transversely in this type of tetrad. Example: Aristolochia & Butomopsis.
(v) Linear tetrad: In this tetrad, all four pollens arranged in linear order. e.g., Halophylla, Halophia.
All the above type of tetrads are found in Aristolochia elegans.
The most common type of tetrads is Tetrahedral.
Q.1. Explain the role of the tapetum in the formation of the pollen-grain wall.
Ans. Tapetum is the innermost wall layer of a microsporangium. It nourishes the developing pollen grains and also helps in the formation of the wall of pollen grains. The cells of tapetum secrete Ubisch granules that provide sporopollenin and other materials for exine formation.
Q.2. Where is sporopollenin present in plants? State its significance with reference to its chemical nature.
Ans. Sporopollenin is present in the exine of pollen grains in plants. It is one of the most resistant organic substances and can withstand high temperatures, strong acids and alkalis. It protects the pollen grains from enzymes and helps them to be well preserved.
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1. What is microsporogenesis? |
2. How does microsporogenesis occur? |
3. What is the significance of microsporogenesis? |
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