Plants and plant bodies exhibit several different variations in the manner they sexually reproduce. Different groups of plants show distinctly different stages in their reproductive cycle: for example the gametophyte and the sporophyte stage.
Gametophytes produce the male and female gametes, which fuse to form a sporophyte. A major part of the plant reproductive organ or gametophyte is the microsporangium, in which the development of pollen grains takes place.
What is Microsporangium?
Male plant gametophytes usually develop and reach maturity in the anther of a plant. The microsporangia are the part of the anther in which the pollen or microspores are produced. To understand this, we first should know what is a microspore.
Microspores are essentially plant spores, that give rise to the male gametophytes, which further develop into sperm cells, which ultimately fuse with the egg cells to form a zygote.
Structure of Microsporangium
Microsporangia are usually bi-lobed structures that function as pollen sacs and are found in the anther of a plant, located at the end of the long filament-like stamen. The structure of microsporangium features a circular outline, surrounded by four layers. These are:
A singular epidermis which stretches and subsequently falls of when it attains maturity.
An endothecium, the cells of which consist of fibrous endings.
The middle layers. The cells in the middle layers usually break down in a fully-developed anther.
A layer of uninucleate, binucleate or multinucleate layers of tapetum that feature a very dense cytoplasm.
The outermost layers of the microsporangium help to protect the microspores and play a crucial role in the release of pollen grains from the anther. The tapetum provides nourishment to the pollen and also contributes some very important parts to the pollen wall.
The following ts of young anther illustrates the many layers of a microsporangium.
Here’s a fun quiz for you to try and revise all that you learnt about the structure of microsporangium.
Pop Quiz 1
The ________ is the outermost layer of a microsporangium.
What is Microsporogenesis?
To define microsporogenesis, it is simply the process by which the pollen mother cells give rise to microspores.
At the centre of each microsporangium in the young anther of a plant, lies a mass of sporogenous tissue. As the anther develops, the sporogenous cells present in the sporogenous tissue form microspore tetrads through meiotic division. Thus each cell is known as the microspore or pollen mother cell. These microspores usually arrange themselves in the form of a tetrad. With the maturation of the anther and subsequent dehydration, the microspores start to detach from each other and develop into full-grown pollen grains.
How are Microsporangium Formed?
The development of microsporangium is a complex biological process that starts with the actively dividing meristematic cells in the young anther of a plant. The anther, a part of the stamen, contains the pollen grains. These meristematic cells are surrounded by a thin layer of epidermis that soon develops into a bi-lobed structure. Each lobe then develops a pair of pollen sacs, and consequently, a two-lobed anther gives rise to four pollen sacs in total. These sacs are located at the four corners of the anthers, and they comprise of cells that divide to form the primary sporogenous layer.
There also lies a simple difference between microsporangia and microsporangium. Microsporangia is a collection of many containers of sporogenous tissue while a single container is called a microsporangium.
A mature pollen grain generally consists of two kinds of cells: a pollen tube cell and a generative cell. The tube cells develop into the pollen tube on successful germination, while the generative cell moves into the ovary via the pollen tube. Generative cells are usually present within a large pollen tube cell and divide to from a couple of gametes or sperm cells inside the tube. On maturation, the anther releases all the pollen grains for fertilisation.
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1. What are microsporangia?
Microsporangia are usually bi-lobed structures that function as pollen sacs and are found in the anther of plant, located at the end of the long filament-like stamen. Male plant gametophytes develop and reach maturity in the anther of a plant. The microsporangia are the part of the anther in which the pollen or microspores are developed.
2. What is microsporogenesis?
Microsporogenesis is the process by which the pollen mother cells give rise to microspores. At the centre of each microsporangium in the young anther of a plant, lies a mass of sporogenous tissue. As the anther develops, the sporogenous cells present in the tissue form microspore tetrads through meiotic division. Thus each sporogenous cell is known as the microspore or pollen mother cell.
3. What are the four main layers of a microsporangium?
The four layers of a microsporangium are:
A singular epidermis
The middle layers
A layer of uninucleate, binucleate or multinucleate layers of tapetum