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प्रश्न
Explain the role of tapetum in the formation pollen-grain wall.
उत्तर
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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संबंधित प्रश्न
(a) Plan an experiment and prepare a flow chart of the steps that you would follow to ensure that the seeds are formed only from the desired sets of pollen grains. Name the type of experiment that you carried out.
(b) Write the importance of such experiments
An anther with malfunctioning tapetum often fails to produce viable male gametophytes. Give any one reason.
A flower of brinjal plant following the process of sexual reproduction produces 360 viable seeds.
Answer the following questions giving reasons:
(a) How many ovules are minimally involved?
(b) How many megaspore mother cells are involved?
(c) What is the minimum number of pollen grains that must land on stigma for pollination?
(d) How many male gametes are involved in the above case?
(e) How many microspore mother cells must have undergone reduction division prior to dehiscence of anther in the above case?
Arrange the following terms in the correct developmental sequence:
Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
Microsporogenesis occurs ______.
Exine of pollen grain is formed of ______.
In a typical complete, bisexual, and hypogynous flower the arrangement of floral whorls on the thalamus from the outermost to the innermost is ______.
Generative cell was destroyed by laser but a normal pollen tube was still formed because ______.
Fertilization involving carrying of male gametes by pollen tube is ______.
Nonessential floral organs in a flower are ______.
In angiosperms various stages of reductional division can best be studied in ______.
______ of the pollen grain divides to form two male gametes.
The three cells found in a pollen grain when it is shed at 3-celled stage are ______.
Pollen kitt is generally found in ______.
Sepals and petals or perianth are inconspicuous in entomophilous flowers.
Meiosis does not occur in the organisms showing haplontic life cycle.
On observing the pollen grain under the microscope, it was found to belong and ribbon shaped. The flower-bearing these pollen grains will be pollinated by: ______
Male gametophyte with least number of cell is present in ______.
Male gametophyte in angiosperms produces ______
