Endothecium

Anther maturation is a complex process involving many metabolic pathways that is connected with the dehiscence and release of pollen grains from the anther. In the endothecium, auxins, jasmonic acid, and lignification of secondary cell walls have a role in determining the transformations that occur. The function of auxins is controlled by the transcription factor MYB26, which is encoded by the MYB26 gene and is found in the lignin biosynthesis pathway. It is necessary to note that the lignification of endothecium walls is accompanied by the removal of the middle layer and tapetum cells, the creation of distinctive thickenings, and the activation of phosphotransfer proteins during this process. Because they act as phosphorelay mediators, these histidine proteins play an important role in the multistep cytokinin-signalling cascade. To this end, the protein CBSX2, which is found in the chloroplast, controls the quantity of H2O2, thioredoxin, and jasmonic acid in the chloroplasts as well as the production of wall evaginations. They are regulated by the ROT VU-B SENSITIVE4 gene, which encodes a protein with the DUF647 domain of an unknown function, which regulates the expression of secondary endothecium cell wall genes.

Role of endothecium

Angiosperm anther structure is usually preserved throughout their evolutionary history. Each of the four layers of the anther wall is referred to as an epidermis, endothecium, middle layer, and tapetum. Pollen mother cells conduct meiosis within anther locules, resulting in the formation of microspores that are encased within the tetrad. Microspores continue to develop after being released, eventually maturing into pollen. The distinct layers of the anther wall perform diverse tasks in the process of pollen production and discharge. When it comes to anther development, the epidermis serves as a protective barrier. The tapetum provides nutrients for the development of microspores as well as ingredients for the creation of pollen walls. When an anther is fully formed, the endothecium is responsible for its dehiscence, which allows pollen to be dispersed. Located between the tapetum and the endothecium, the middle layer is a layer of tissue. Currently, there is little understanding of its formation and function during the process of anther development.

Dehiscence

Dehiscence is the splitting of a mature plant structure along a naturally occurring line of weakness in order to liberate the contents of the structure. This is frequent in fruits, anthers, and sporangia, among other things. Sometimes this entails the total detachment of a component; structures that open in this manner are referred to as dehiscent structures. Structures that do not open this way are referred to as indehiscent, and they rely on other mechanisms to discharge their contents, such as disintegration or predation.

The opening of some flower buds (e.g., Platycodon and Fuchsia) is a process that is comparable to dehiscence, but it is rarely referred to as dehiscence unless it involves circumscissile dehiscence; anthesis is the term used to refer to the opening of flowers in general. Dehiscence may or may not result in the loss of a structural element as a result of the abscission process. The caducous structures are those that have been lost.

Anther dehiscence

Anther dehiscence is the ultimate function of the anther, and it is this process that results in the discharge of pollen grains from the anther. This procedure is meticulously synchronised with pollen differentiation, floral development, and flower opening to ensure a successful outcome.

One of the walls of the anther wall fractures at a specified location. It is usually observed as a depression between the locules of each theca that extends the whole length of the anther, but in species with poricidal anther dehiscence, it is actually a tiny hole. This is referred to as extrorse dehiscence when the pollen is released from the anther through a split on the outer side of the flower (relative to the centre of the bloom), and this is referred to as introrse dehiscence when the pollen is released from the interior side of the flower. Latrorse dehiscence is a type of pollen release in which the pollen is expelled through a split that is positioned to the side, towards other anthers, rather than towards the inside or the exterior of the flower. When an anther is dehisced, the stomium is the area where the dehiscence takes place. This process of cell degeneration in the stomium and septum cells occurs in accordance with the developmentally scheduled cell death programme. Dehiscence is also dependent on the expansion of the endothelial layer and the subsequent drying of the wound. In the endothecium, the tensions that cause the anther to divide are caused by the contraction of the tissue. This tissue is typically one to several layers thick, with cell walls that are unevenly thickened as a result of unequal lignification throughout the tissue. The cells lose water, and the uneven thickness of the cells’ walls leads the thinner walls of the cells to stretch to a larger amount than the thicker walls of the cells. Eventually, because of the buildup of strain, the anther is split along its line of weakness, resulting in the release of pollen grains into the surrounding environment.

Conclusion

When an anther is fully formed, the endothecium is responsible for its dehiscence, which allows pollen to be dispersed. In angiosperms, the layer of cells that lies beneath the epidermis of the wall of the anther is referred to as the anther epidermis. As the anther grows, thickenings in the cell walls of the endothecium are common, and these thickenings are thought to aid in dehiscence. Located between the tapetum and the endothecium, the middle layer is a layer of tissue.

Microsporangium is typically surrounded by wall layers such as the epidermis, endothecium, two or three intermediate layers, and the tapetum, among other things. Endothecium serves as a protective layer and aids in the dehiscence of another to allow the discharge of pollen from the plant.