Reproduction is the means of maintaining the survival and existence of species, generation after generation. Flowering plants exhibit sexual reproduction and have sophisticated male and female reproductive units as well as accessory structures. Microsporogenesis is the process of forming and differentiating microspores (pollen grains) from microspore mother cells(MMC) by the process of reductional division. To create a microspore tetrad, sporogenous tissue cells divide by meiosis. The microspore separates and transforms into pollen grains when the anther ages and dries up.
Male gametes, also known as microspores, are produced when minute structures in plants called microsporangium (plural: microsporangia) germinate. Tracheophytes, which produce two distinct sizes or sexes, contain microsporangium. Examples include water ferns and seed plants (spermatophytes, the plants that generate seeds, thus the term, i.e., seed plants), which are spermatophytes.
According to the definition of a microsporangium, a stamen is diploid in microspores like other mother cells and produces four haploid microspores through a process known as meiosis. Meiosis is a special type of cell division that produces gametes such as sperm in males and egg cells in females. These develop into pollen grains, where the microspores multiply twice to form gametes.
The following points briefly describe the structure of microsporangium:
The stamen, which has a bilobed anther connected to the filament, is the flower's male reproductive organ.
Each of the anther's two lobes, which are bifurcated, contains two pollen sacs or microsporangia.
Numerous pollen grains can be found inside the microsporangia.
A bilobed anther's pollen sacs or microsporangia appear to be located at the anther's four corners. As a result, angiosperm anthers are tetrasporangiate.
A connective tissue that houses the vascular bundle that transports nutrients connects the two lobes of the anther.
The exterior wall and the central homogenous sporogenous tissue make up each microsporangium (or pollen sac).
The epidermis (common anther covering), endothecium, 1-3 layer thick middle layers, and innermost tapetum are the four different types of layers that make up the Microsporangium wall.
The endothecium, intermediate layers, and epidermis all serve as barriers of defence. The endothecium aids in the release of pollen grains during the ripe anther's dehiscence.
At maturity, the central layer starts to deteriorate.
The developing pollen grains are fed by the tapetum, which is the innermost wall layer. The thick cytoplasm and many nuclei are characteristic of tapetum cells.
Sporogenous cells, also known as microsporocytes, are tightly packed together at the microsporangium's centre. A microsporocyte has a large nucleus and lots of cytoplasms.
Process of Microsporogenesis in Plants
The following are the steps of microsporogenesis:
The whole core of a microsporangium is filled with sporogenous tissue, also known as microsporocytes, whose cells multiply together with the anther's expansion.
Each microsporocyte passes through mitosis and divides to create a number of diploid microspore mother cells (MMC) or pollen mother cells (PMC).
The plasmodesmatal connections between the microspore mother cells are broken when the cells acquire an interior layer of callose (-1,3 glucan).
Tetrads of haploid microspores or pollen grains are created by the meiosis of the divided mother cells, which round out and separate. Microsporogenesis is the name of this phenomenon.
Tetrads can be classified into five different shapes: isobilateral, tetrahedral, decussate, T-shaped, and linear. A tetrad's pollen grains develop and separate from one another. The most typical sort of microspore configuration in a tetrad is either isobilateral or tetrahedral. Decussate, linear, and T-shaped tetrads are also discovered, though.
The male gametophyte's first cells are found in the pollen grains.
Tetra-sporangiate or dithecous microsporangia make up a whole anther's four microsporangia. Some plants have a single lobe with two monothecous or microsporangia (for instance, Hibiscus, Moringa, and the Malvaceae family). Rarely does an anther have a single microsporangia unisporangiate on just one lobe (for example, Arceuthobium).
Gametes (known as microsporocytes) that are capitulating microspores are produced by the male microsporangia. The female portion of megasporangia, on the other hand, creates gametes (megasporocytes) that aid in the production of megaspores. Since the pollen grain is the successor to the Microsporangium, which is where pollen sacs are always thought to be carried, the development of microsporangium and pollen grain plays a significant part in reproduction.
1. Explain the dehiscence of the anther.
The sterile strip that was present between the two pollen sacs of each anther lobe separates to form a single cavity as the mature anther dries up. The endothecium's variably thickened dead cells contract from their outer thin walls and become concave as a result of water loss. The outer radial walls get closer as a result. As a result, the endothecium shortens and ruptures the anther lobe wall in the vicinity of the stomium. The various organisations collect the exposed spores for pollination.
2. What is the difference between microsporogenesis and megasporogenesis?
Two processes that take place in seed plants are microsporogenesis and megasporogenesis. Male and female spores are referred to as microspores and megaspores, respectively. Microsporangia, which are 2n cell-sized structures, are found in the anthers of stamens. Microspores, which are n cells, are produced by the meiosis of the microspore mother cells. This process is referred to as microsporogenesis.
Pollen grains, which are male gametes, are produced by the mitotic division of microspores. Ovules are what megasporangia are. Megaspore mother cells are found in ovules. Megaspores, which are n cells, are produced when the megaspore mother cells undergo meiosis and divide. Megasporogenesis is the process by which megaspores develop from megaspore mother cells. Megaspores go through mitosis and produce egg sacs. This is how microsporogenesis and megasporogenesis differ from one another.
Megasporogenesis Flow Chart
3. What is the viability of a pollen grain?
The length of time that pollen grains remain viable is highly variable and, to some extent, is determined by the temperature and humidity conditions that are now in effect. After being released into the air, the pollen grains of some cereals, such as rice, and wheat, lose their vitality after just 30 minutes. It is possible for pollen grains to retain their vitality for several months in certain Rosaceae, Leguminosae, and Solanaceae species. It is feasible to preserve pollen grains from a wide variety of species for an extended period of time in liquid nitrogen, which has a temperature of -196 degrees Celsius.