Name: Dissection of Dicot Seed
Uploaded: 2019-07-19
Duration: 4 min 14 s
Description: Seeds are protected by seed coats that can be easily removed by soaking. An embryo can be seen slightly pointing out of the cotyledons. Let's take a close lo...

Question

With the help of a well-labelled diagram, describe the development of a male gametophyte of an angiosperm. What is sporopollenin.

Accepted Answer

In angiosperms, the pollen grains are called male gametophytes that bear male gametes. The development of pollen grains takes place inside the microsporangia. The formation of microspores or pollen grains from microspore mother cells or pollen mother cells is called microsporogenesis.

Sporogenous tissue fills the whole interior of a microsporangium. Its cells divide with the growth of anther and increase their number. Ultimately they are transformed into microspore or pollen mother cells (PMC). The latter are diploid, that is, they possess two genomes or sets of chromosomes. These microspore mother cells undergo meiosis to produce tetrads of microspores or pollen grains. Usually, the arrangement of microspores in tetrad is tetrahedral or isobilateral.

As the anther matures, the microspores dissociate from tetrads and develop into pollen grains. During the growth of the pollen grains, vacuoles develop, it pushes the nucleus to one side near the wall. The protoplast then divides mitotically to form two unequal cells- a small generative cell and a large vegetative or tube cell. In some species, the generative cell divides into two nonmotile male gametes before the dehiscence of anther and the release of the pollen grains. Therefore, at the time of pollination, the pollen grain is either two-celled (generative cell + vegetative cell) or 3 celled (vegetative cell + two male gametes).

Each pollen grain has a double-layered wall called sporoderm. The outer layer of the pollen wall is thick, highly resistant, and is called exine that contains sporopollenin. It is one of the most resistant organic compounds that protects pollen grains from external factors. Because of sporopollenin, pollen grains are preserved as fossils.The inner layer of sporoderm is called intine.

With the help of a well-labelled diagram, describe the development of a male gametophyte of an angiosperm. What is sporopollenin.

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