Microsporangium – Structure and Function

Plants are living like all of us are aware of; they breathe, respirate, reproduce and even tend to have the feeling of senses in some cases. There are many species of plants, and every species will have different types of respiratory functions, and so will be the reproductive ones. Before that, one needs to understand the basic parts of the plants involved in the process. Microsporangium (plural microsporangia) are microscopic structures in plants that give rise to gametes (here, the gametes are male, also called microspores) when they germinate. Microsporangium occurs in Tracheophytes, which produce two different sizes or sexes. Some of the examples include seed plants (spermatophytes, the plants that produce seeds, hence getting its name, i.e., seed plants), and other aquatic fern plants. Microsporangium definition stamen is diploid in microspores like other mother-cells, producing four haploid microspores through a process called meiosis (Meiosis is a unique type of division of cells (especially germ cells) which are used to produce gametes, like sperm in males and egg cells in females). These further become the pollen grains, in which the microspores distribute doubly to produce gametes.

Microsporangium Structure

Microsporangium is generally structured, having two lobes (Bi-lobed) that function as pollen sacs. The structure of Microsporangium consists of a round circular outline, covered by four layers. Namely: –

1. A singular epidermis elongates and eventually falls off the plant when it reaches the stage of maturity.
2. Endothecium- cells contain fibrous endings.
3. Middle Layers- these usually break off in fully developed and matured anther.
4. Then comes the layer of uninucleate (single), binucleate (two) or multinucleate (many) layers of the innermost cell layer in the anther, also called the tapetum.

The outermost layers of the Microsporangium protect the microspores. They play an efficient role when there is the release of pollen grains from the anther. The tapetum ensures the sustenance of the pollen and assures the important role-play at the major part of the pollen wall.

In young anther, one can find the sporogenous tissue in the centre of microsporangium. As the anther develops, the sporogenous tissue present in the centre of the anther undergoes meiotic division to form microspore tetrads. Each sporogenous tissue we call a pollen mother cell or microspore mother cell. The process of formation of microspore from the pollen mother cell is known as microsporogenesis. Usually, microspores are arranged in the form of tetrads. The pollen grain is developed when the anther matures and dehydrates.

There are two types of cells present in the matured pollen grains. They are generative cells and pollen tube cells. On germination, a pollen tube is formed from the tube cells. Through the pollen tube, the cell migrates into the ovary. The generative cells divide into two gametes or sperm inside the pollen tubes.

The Functional gametes 

The microsporangia (male) produce gametes (called microsporocytes) that are capitulating microspores. On the other hand, the female part megasporangia produce gametes (megasporocytes) that help in the yielding process of megaspores. The Microsporangium and pollen grain play a major role in reproduction as the latter is the successor of the other one, and pollen sacs are always considered borne on the lower areas in Microsporangium. The stamen consists of spore cases that further develop microspores, also called potential pollen grains. Each ovule in the pistils enclose an egg, and when that microspore germinates into the pistil with the egg, it is called a pollen grain.

Formation of microsporangia

The formation starts with the division of meristematic cells in the centre of the anther. The epidermis is the thin layer surrounding the meristematic cells, becoming a bilobed structure. Each lobe turns out into a pollen sac, and this bilobed anther gives rise to four pollen sacs. At the corner of the anther, one can find the pollen sac. Each pollen sac consists of cells that divide and form a primary sporogenous layer.

There is a major difference between microsporangia and microsporangium. The collection of sporogenous tissue is called microsporangia, and the microsporangium refers to the single sporogenous tissue.

Pollen grains

There are two types of cells present in the matured pollen grains. They are generative cells and pollen tube cells. After germination, the tube cells develop into pollen tubes. Generative cells are present on a large pollen tube, which divides to form gametes or sperm inside the tube. The anther releases the pollen grains to fertilise with the egg on maturation. During microsporangium, pollen grains develop, and it is considered an important part of reproduction.

Conclusion

Microsporangium is microscopic structures in plants that give rise to gametes when they germinate. They occur in tracheophytes, which produce two different sizes or sexes. One such example of microsporangium is spermatophytes; they are the plants that produce seeds; therefore, these are known as seed plants, and other ones are the aquatic fern plants. They generally have structures with two lobes, i.e., Bi-lobed. The structure of the microsporangium is the singular epidermis, endothecium, middle Layers and outermost layer. The outermost layer is used to protect the microspores. It has the male part as microsporangia and the female part known as megasporangia.