The key difference between microspore and pollen grain is that microspore is the small spore that develops into the male gametophyte in plants while pollen grain is the small grain that contains the male gametophyte.
Plant reproduction takes place both sexually and asexually, showing the alternation of generation. There are two generations known as sporophytic generation and gametophytic generation. Microspore and pollen grain are two structures that develop during these two generations. Microspore is a structure of sporophytic generation, whereas pollen grain is a structure of gametophytic generation. Also, the microscope is not a gametophyte while pollen grain is a gametophyte.
CONTENTS
1. Overview and Key Difference
2. What is Microspore
3. What is Pollen Grain
4. Similarities Between Microspore and Pollen Grain
5. Side by Side Comparison – Microspore vs Pollen Grain in Tabular Form
6. Summary
What is Microspore?
There are two types of spores produced in heterosporous land plants. They are megaspores and microspores. The megaspore develops into the female gametophyte, whereas the microspore develops into the male gametophyte. Thus, microspores, link sporophytic generation and gametophytic generation during the alternation of generations. The gametophyte developed through microspore then produces the male gametes. The male gametes participate in sexual reproduction of plants. Finally, the microspore develops into the pollen grain, which is the actual male gametophyte.
Figure 01: Life Cycle of an Angiosperm
Haploid microspores are present in the microsporangia inside the modified leaves called microsporophylls. The diploid microsporocytes produce microspores through meiosis. The structure of the microspore consists of three layers. They are the outer cover layer called the perispore, the middle layer called the exospore, and the inner layer is called the endospore.
What is Pollen Grain?
The pollen grain is the actual male gametophyte. Therefore, it develops from the microspore. Actually, it is the reduced form of male gametophyte. It is present only in seed plants: angiosperms and gymnosperms. The development of pollen grains from microspores takes place through the process of microgametogenesis. Meiosis is the principle phenomenon in pollen grain development.
Figure 02: Pollen Grains
Each pollen grain consists of four cells and a pair of air sacs situated externally. In flowering plants, the pollen grains are present in sacs in the anther. They are haploid cells. They transfer to the female gametophyte during pollination. Thus, this results in the fertilization process.
What are the Similarities Between Microspore and Pollen Grain?
- Microspore and pollen grain are produced by the process of meiosis.
- Both produce via microsporocytes.
- Moreover, both are found in heterosporous plants.
- Also, both result in forming the male part (male gametangia) of the plant during sexual reproduction.
- Besides, they are haploid in nature.
- Additionally, both are small structures.
What is the Difference Between Microspore and Pollen Grain?
The key difference between microspore and pollen grain is based on the gametophyte. That is; the microspore develops into the male gametophyte while the pollen grain contains the male gametophyte. Furthermore, microspores develop only via meiosis, whereas pollen grains develop via meiosis and then undergo mitosis. In this regard, this is also a difference between microspore and pollen grain.
Moreover, a further difference between microspore and pollen grain is that even though both cells are haploid in nature, microspore is unicellular, whereas pollen grains are multicellular.
The below infographic presents more information regarding the difference between microspore and pollen grain.
Summary – Microspore vs Pollen Grain
Microspore and pollen grain are important structures in the reproduction process of vascular plants. The microspore develops via microsporogenesis. When the conditions are optimal, the microspores develop into male gametophytes known as pollen grains. In this regard, the pollen grain is the male gametophyte that contains male gametes for sexual reproduction. Therefore, microspores act as the main link between the sexual and the asexual reproduction in plants. Thus, this summarizes the difference between microspore and pollen grain.
Reference:
1. “FLOWERING PLANT REPRODUCTION: Fertilization and Fruits.” Flowering Plant Reproduction II, Available here.
Image Courtesy:
1. “Angiosperm life cycle diagram-en” By LadyofHats Mariana Ruiz – did it myself based in at least 5 illustrations but mainly on a image from Judd, Walter S. , Campbell, Christopher S. , Kellog, Elizabeth A. andStevens, Peter F. 1999. Plant Systematics: A PhylogeneticApproach.Sinauer Associates Inc.ISBN 0-878934049. (Public Domain) via Commons Wikimedia
2. “Passiflora Pollen Grains” By Asja Radja – Own work (CC BY-SA 4.0) via Commons Wikimedia