The anther is a floral structure located in the terminal portion of the stamen or male reproductive organ. Each anther, which is divided into lobes or portions called theca, is responsible for the production of pollen and its release.
It is a key element in the pollination process and can vary widely in structure and arrangement, depending on the plant group.
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characteristics
The anther is the bulging region found in the final region of the stamen in the flowers of angiosperms, in the image they are seen as elongated sacs with orange tones.
Teak can be arranged spatially as follows: if one is opposite the other they are called divergent, if they are sloping they are oblique, if one is opposite the other it is parallel, and transverse if they are opposite and horizontal..
Parts
Stamen
Before describing the structure of the anther, it is necessary to mention the organization of the male reproductive organ: the stamen.
A stamen is divided into two parts: a filament and the anther. The former is relatively simple in structure, with an epidermis that presents trichomes and stomata and a uninervated system - there is only one vascular bundle that runs through the structure.
The stamen is classified according to the fusion of its elements. We have separate stamens and in a single whorl called haplostémonos. The didelfos have two groups of stamens fused at the level of the filaments.
Similarly, monodelphs are defined as a group of united stamens. Polydelphs have some groups of stamens connate by their filaments. Finally, if the anthers are fused, the androecium is syngeneic.
Anther
The structure of the anther is a bit more complex. In most plants, the anther divides into two lobes called "teak." Inside each teak, the two pollen sacs or microsporángios are observed, where the formation of pollen grains occurs.
To count the number of teak, it is recommended to do it just at the moment of the flower opening, since after this event deformations occur that greatly hinder its observation.
Two pollen sacs are found in the anthers that have only one teak. As an example of monothetic anthers - a teak - we have the genera belonging to the Malvaceae family: Hibiscus, Malva, Sida and Gossypium.
The portion of the stamen that joins both theca is called connective. In the dorsifix type anthers the portion of the filament is welded to the connective, causing the anther to rotate on it.
This phenomenon is known as a versatile anther and is seen in plants of the Poaceae family, such as Hemerocallis and Agapanthus. The stamen is sessile when the filament is short.
Anther Anatomy
The outermost section of the anther is made up of a single layer of epidermis, followed by another layer of endothecium that appears to be well developed when the anther is mature. Endothecium helps the dehiscence of pollen grains.
Continuing inside the anther are three to four layers, where the innermost one surrounds the microsporangium and is the tapetum layer. This section has the function of nourishing the mother pollen and the small microspores. Similarly, the outer wall of the pollen is synthesized by the tapetum.
The cells of the tapetum exhibit a wide variety of cell division systems, such as endomitosis, normal mitosis, and a particular type of nuclear division where chromosomes divide but the nucleus does not, resulting in polynucleated cells.
The anther presents a procambial strand located in the central region, which is responsible for forming the vascular bundles.
Features
Flowers are the organs of plants responsible for reproduction. Structurally, the flowers have sterile segments whose main function is the attraction to pollinators and the protection of the sexually active elements: the stamens and the pistil.
The stamens represent the male organs of the flowers. In angiosperm plants, the terminal portion of this floral structure is called the anther, whose main function is the production of pollen.
The pollen
Pollen is the set of microscopic grains that contain inside a male gametophyte, which represents the haploid phase of the typical life cycle of plants.
They are composed of membranes that function as bags and store the spermatic fluid inside, which is generally a yellow corpuscular dust. When they come into contact with water, they hydrate and when they burst they release an oily substance that contains microscopic bodies called fovilla.
When the pollination process occurs and the pollen grain manages to reach the stigma, it germinates. A pollen tube emanates from this small grain, through which the male nuclei move towards the oosphere or female gamete.
Pollination may occur by wind. For this reason, the plant must somehow compensate for the stochastic dispersal mechanism, and it does so by producing huge amounts of pollen. Some plants use water as a dispersal medium.
However, the most popular pollinating agent in angiosperms is animals, call it insects, birds, or bats, which transfer pollen directly to other flowers.
Pollen release
The dehiscence or release of pollen occurs thanks to an uneven thickening of the endothecium. The internal structure is thicker and, as we move to the external face, we find a reduction in cells.
When the cells become dehydrated, they create a tension that favors the opening of the anther. This phenomenon is one of the most important functions of the anther and is synchronized by pollen differentiation events and floral development.
Opening can occur in different ways: longitudinal or transverse. Following the direction of the filaments in the opening process, the process can be classified as: introsal dehiscence (towards the interior to bloom, favoring self-pollination) or extruded dehiscence (towards the outside, favoring pollination between different individuals).
Dehiscence can also occur through pores or - called poricidal - or by the opening of valves present in theca.
References
- Khan, A. (2002). Plant anatomy and physiology. Gyan Publishing House.
- Mishra, SR (2009). Understanding Plant Anatomy. Discovery Publishing House.
- Montiel, M. (1991). Introduction to the flora of Costa Rica. Editorial University of Costa Rica.
- Pandey, SN, Pandey, SN, & Chadha, A. (1993). A Text Book Of Botany: Plant Anatomy and Economic Botany (Vol. 3). Vikas Publishing House.
- Plitt, JJ (2006). The flower and other derived organs. Caldas University.
- Weberling, F. (1992). Morphology of flowers and inflorescences. CUP Archive.