Difference Between Microsporogenesis and Microgametogenesis

Key Difference – Microsporogenesis vs Microgametogenesis
 

The reproductive unit of angiosperms is the flower. A flower consists of two reproductive units; androecium and gynoecium. Androecium is the male reproductive unit whilst the gynoecium is the female reproductive unit. The androecium contains anther and filament and the gynoecium contains stigma, style, and ovary. Microsporogenesis and microgametogenesis take place in the anther of the androecium. Microsporogenesis is the process of formation of pollen grains (microspores) from sporogenous tissue and microgametogenesis is the process of formation of male gametes from the generative cell nucleus that is present inside the pollen grain through mitosis. This is the key difference between Microsporogenesis and Microgametogenesis.

CONTENTS

1. Overview and Key Difference
2. What is Microsporogenesis
3. What is Microgametogenesis
4. Similarities Between Microsporogenesis and Microgametogenesis
5. Side by Side Comparison – Microsporogenesis vs Microgametogenesis in Tabular Form
6. Summary

What is Microsporogenesis?

Microsporogenesis is a process that takes place during plant reproduction. As a general fact, during this process, a microgametophyte develops inside a pollen grain. This development takes place in a three-celled stage. With regards to flowering plants; angiosperms, the microsporogenesis process takes place with the involvement of a microspore mother cell. The microspore mother cell is present in the anther of the flower, which is one of the two segments of the androecium (male reproductive unit of the angiosperm flower).

Under a cross-sectional examination, the anther appears with two distinct lobes. Each lobe consists of two microsporangia (thecae). A single anther is composed of 04 microsporangia. There are 4 fertile cell layers in each microsporangium. They are (from outside to inside), epidermis, endothecium, middle layers and tapetum. These cells are known as sporogenous cells. The outer most layer, which is the tapetum, consists of sterile cells. The function of the tapetum is to provide nourishment to developing pollen grains.

Other three types of sporogenous cells that develop into microspore mother cells are diploid (2n). These microspore mother cells are also referred to as microsporocytes. These microsporocytes undergo meiotic division to become four (04) microspore cells that are haploid (n). The tube cell and the generative cell are developed through mitotic division of these haploid microspore cells.

What is Microgametogenesis?

Microgametogenesis is a process by which progressive development of the unicellular microspores takes place where they get developed to mature microgametophytes containing gametes.  The development phase of microspores takes place with the onset of expansion of microspore. In this phase, a single large vacuole is produced within the microspore cell. The formation of the vacuole results in the movement of the nucleus of the microspore to an eccentric position. The displacement of the nucleus occurs against the wall of the microspore cell. At this position within the cell, the nucleus undergoes mitosis.

Figure 01: Microgametogenesis as a part of Angiosperm Life Cycle

This mitotic division is referred to as pollen mitosis I (first pollen mitosis). Here, through this division, 4 different cells are produced. They include two unequal cells, a small generative cell, and a large vegetative cell. These cells contain a haploid nucleus.  The generative cell will get detached from the wall of the pollen grain. The fate of the generative cell is decided by the large vegetative cell that engulfs it. This results in the development of a unique structure that is a cell within a cell. The engulfed generative cell the mitotically divides. This division is referred to as pollen mitosis II (second pollen mitosis). The result of this mitotic division is the or two male gametes.

What are the Similarities Between Microsporogenesis and Microgametogenesis?

• Both Microsporogenesis and Microgametogenesis processes take place inside the angiosperm flower.
• Both Microsporogenesis and Microgametogenesis involve haploid cell formation.
• During microsporogenesis and megasporogenesis, spores that give rise to gametophytes are produced.

What is the Difference Between Microsporogenesis and Microgametogenesis?

Summary – Microsporogenesis vs Microgametogenesis

Microsporogenesis is a process of formation of pollen grains (microspores) from the sporogenous tissue. As a general fact, during this process, a microgametophyte develops inside a pollen grain. This development takes place in a three-celled stage. Microgametogenesis is a process by which progressive development of the unicellular microspores takes place where they get developed to mature microgametophytes which contain gametes. Two types of mitotic divisions take place; pollen mitosis I and pollen mitosis II. The results of the pollen mitosis I are two unequal cells, a small generative cell, and a large vegetative cell. The results of pollen mitosis II are the formation of two sperm cells. This is the difference between microsporogenesis and microgametogenesis.

Reference:

1.“Medicinal Plants Archive.” Microsporogenesis and Microgametogenesis – Pollen Grains. Available here
2.Tang, Ya, et al. “Microsporogenesis and microgametogenesis of Excentrodendron hsienmu (Malvaceae s.l.) and their systematic implications.” Botanical Journal of the Linnean Society, vol. 150, no. 4, 2006, pp. 447–457., doi:10.1111/j.1095-8339.2006.00476.x

Image Courtesy:

1.’Angiosperm life cycle diagram-en’By LadyofHats Mariana Ruiz – Own work,  (Public Domain) via Commons Wikimedia 

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