In plants, hormonal and structural changes lead to the differentiation and development of floral primordium, which is the first stage of flowering. The following sections describe the structures and events that take place during prefertilization.
Male reproductive part androecium:
Stamens are the building blocks of the androecium. Each stamen is comprised of two parts: an anther and a filament. The male gametophyte is represented by the pollen grains produced by the anther.
Development of anther:
At the beginning of its development, and anther is a homogeneous mass of cells surrounded by an epidermis. During its development, the anther develops into a four-lobed structure. In each lobe, a row or a few rows of hypodermal cells become enlarged, with prominent nuclei, as a result of the enlargement. This serves the purpose of an archesporium.
During periclinal divisions, the archesporial cells divide to form primary parietal cells that migrate towards the epidermis and primary sporogenous cells that migrate towards the inner side of the anther. After going through a series of periclinal and anticlinal divisions, the primary parietal cells divide again to form anther walls, which are composed of endothecium, middle layers, and tapetum layers, which are arranged from the periphery to the centre.
MicroSporogenesis:
Microsporogenesis is the term used to describe the stages involved in the formation of haploid microspores from a diploid microspore mother cell through the process of meiosis. The primary sporogenous cells may form sporogenous tissue on their own, or they may undergo a few mitotic divisions before forming sporogenous tissue. It is the final generation of sporogenous tissue that performs the function of microspore mother cells. Each microspore mother cell undergoes meiotic division, resulting in the formation of a tetrad of four haploid microspores (microspore tetrad).
A short time later, microspores separate from one another and remain free in the anther locule, where they mature into pollen grains. In some plants, a microsporangium, which contains all of the microspores, remains intact and is referred to as a pollinium.
Take, for example, Calotropis. Pollinia are attached to a sticky structure that looks like a clamp or clip, which is known as the corpuscular. The retinaculum is the filamentous or thread-like part of each pollinium that emerges from the centre of the flower. The entire structure, which resembles an inverted letter ‘Y,’ is referred to as a translator.
Anther wall:
This structure is comprised of the following layers in its mature state
- The epidermis; b. The endothecium; c. The middle layers; and d. The tapetum.
- The Epidermis:
It has a single layer of protection and serves a protective purpose. Anticlinal divisions are performed repeatedly by the cells to keep up with the rapidly expanding internal tissues.
- Endothecium:
It is typically comprised of a single layer of radially elongated cells that lies beneath the epidermis. The inner tangential wall develops bands of cellulose (and, in some cases, radial walls as well) that are visible from the outside (sometimes also slightly lignified). The cells have a high hygroscopicity. Endothecial differentiation is absent from the anthers of aquatic plants, saprophytes, cleistogamous flowers, and extreme parasites, among other things.
These thickenings are absent from the cells that line the junction of the two sporangia of an anther lobe. Stomium is the name given to this region. The presence of this region, combined with the hygroscopic nature of the endothecium, contributes to the dehiscence of the anther at maturity.
- Middle layers:
Middle layers are made up of two to three layers of cells that lie between the endothecium and the epithelium. They are typically fleeting. During maturity, they either disintegrate or are crushed.
- Tapetum:
The anther wall’s first layer is the most inner of the three layers, and it grows to its fullest extent during the tetrad stage of microsporogenesis. A portion of it is derived from the peripheral wall layer, and a portion is derived from the connective tissue of the anther that lines the anther locule. As a result, the tapetum has two points of origin.
As the sporogenous tissue develops, microspore mother cells and microspores are produced in large quantities. The cells of the tapetum may remain uninucleate, or they may contain more than one nucleus or the nucleus may become polyploid, depending on their state of differentiation.
Development of male gametophyte:
This is the first cell of the male gametophyte and it is haploid, making it the microspore. During the time that they are in the microsporangium, male gametophytes can develop and reproduce. During the mitotic division of the microspore, the nucleus divides into two parts: a vegetative nucleus and a generative nucleus.
During the formation of two unequal cells, a large irregular nucleus bearing an abundant food reserve, known as the vegetative cell, and a small generative nucleus, known as the generative nucleus, are formed around the generative nucleus.
In most cases, the pollens are released from the anther during this 2 celled stage. In some plants, the generative cell undergoes a second division, resulting in the formation of two male gametes. During the 2 celled stages, the pollen is released. Pollen is liberated in the 2 celled stages of development in 60% of angiosperm species.
Conclusion:
Pre-fertilization events are the events of sexual reproduction that take place before fertilisation and take place before fertilisation.
At the beginning of its development, and anther is a homogeneous mass of cells surrounded by an epidermis. Microsporogenesis is the term used to describe the stages involved in the formation of haploid microspores from a diploid microspore mother cell through the process of meiosis. This is the first cell of the male gametophyte and it is haploid, making it the microspore. During the time that they are in the microsporangium, male gametophytes can develop and reproduce.