An Introduction to Pollen Grains
Angiosperms, or flowering plants, have produced pollen grains and ovules in specialised structures called flowers, unlike gymnosperms, which have naked ovules. In angiosperms, fruits enclose the seeds. The angiosperms are a category of plants that span a very wide variety of habitats. They come in a variety of sizes, from the virtually microscopic Wolfia to the huge Eucalyptus trees (over 100 meters). They give us fuel, food, medicine, and a number of other vitally necessary goods. A pollen grain is a small structure that contains an androecium, which is a flower's male reproductive system.
Pollen Grain Definition
Pollen grains of a flower are small structures that contain androecium, a flower's male reproductive organ. The pollen grain's interior region comprises cytoplasm as well as the tube cell, which transforms into a pollen tube, and the generative cell, which releases the sperm nuclei.
Pollen grains are structures on a tiny scale that range in both their size and their form. In general, the size of individual pollen grains varies depending on the species and can range anywhere from three to two hundred micrometers (also written as microns). The pollen grain can have a variety of shapes, including a bean shape, a spherical shape, an ovule-shaped form, a triangular shape, a disc-shaped shape, or a triangle shape with a smooth to spiky texture.
Structure of Pollen Grain
Pollen Grains Diagram
Pollen is a mass of microspores found in seed plants that appears as fine dust.
Each pollen grain is a tiny body of different shapes and structures that forms in the male structures of seed-bearing plants and is transferred to the female structures by various methods (wind, water, insects, etc.) where fertilisation takes place.
Pollen is produced by the anthers of the stamens in flowers in angiosperms. It is generated in the microsporophylls of the microstrobili of gymnosperms (male pollen cones).
One or more vegetative cells along with a reproductive cell make up pollen. The male gamete is not found in the pollen grain.
The vegetative cell generates the pollen tube that expands to meet the unfertilized ovules in angiosperms and certain gymnosperms, and the reproductive cell is the source of sperm.
There are three parts to pollen grains.
The source of nuclei for fertilisation is in the middle cytoplasmic portion.
An inner layer, the intine, and an outer layer, the exine, are the other components of the grain wall.
The intine is made up of cellulose or hemicellulose, at least in part.
The exine, the outermost and most lasting layer, is extremely resistant to disintegration; it is unaffected by extreme heat, powerful acids, or strong bases. The exine's constituents are known as sporopollenin.
The pollen grain's internal sections are easily broken down, whereas the exine layer, and hence the pollen grain's general form, is easily preserved in various types of sediments; the quality of preservation varies depending on the environment.
Formation of Pollen
Pollen formation is a complex process. The stamen is the male component of blooming plants. This is made up of an anther and a filament, which is a single stalk. The pollen sacs, which are responsible for manufacturing pollen grains, are frequently found in the anther. Each pollen grain is made up of two male gametes in a single cell. When the anther is fully grown, it breaks open, and pollen is discharged. Fertilisation involves both male gametes, culminating in the production of a zygote and endosperm. Flowering plants are the only ones that go through this process of double fertilisation.
Types of Pollen Grains
Pollen grains can be generated in a variety of ways. The orientation of the furrows about the original tetrads from the microspores can be used to classify pollen grains.
These can be sulcate or colpate.
The furrow in the Sulcate runs across the centre.
The monosulcate sulcus is one, the bisulcate sulcus is two, and the polysulcate sulcus is more than two.
A furrow runs through the colpate in places other than the centre of the outer face.
They are syncolpate if they have two or more fused ends and polycolpate if they do not have two or more fused ends.
Certain pollen grains may be tricolpate pollen grains. This indicates that they have three colpi or have a morphology that is comparable to tricolpate pollen.
Functions of Pollen Grain
Pollen grains are haploid microgametophytes that transport male reproductive cells (gametes) in a plant. The transfer of male gametes to female counterparts (ovules – female reproductive cells) in the embryo sac is their primary function. As a result, sexual reproduction in the plant is made easier. Pollen grains and their diversity play a critical role in the taxonomic classification and phylogeny of higher plants.
Other than these functions, pollen grains also serve the following purposes:
Nutrition: Despite the popular belief that bees are the only pollen-consuming arthropods, pollen-eating species can be found in almost every class of predatory and parasitic arthropods. Pollen is consumed by many Hymenoptera species other than bees as adults, but only a tiny number of Hymenoptera species feed on pollen (including some ant larvae).
Humans: Bee Pollen is sold as a food ingredient and a dietary supplement for human use. Carbohydrates are the most abundant component, with protein content ranging from 7% to 35% depending on the plant type collected by bees.
Forensic Science: Pollen can reveal a lot about where a person or object has been in forensic biology because different parts of the world, or even more specific locations, such as a specific clump of bushes, have different pollen species. Pollen evidence can also identify the season in which a specific object was pollinated.
Conclusion
Studying pollen discovered in sediments and sedimentary rocks allows us to learn a variety of things about deep time because pollen grains are so distinctive and their outer coating (known as exine) is so strong and long-lasting. Palynology is the study of pollen and other particles. Pollen is a food source for some animals, both pollinators and non-pollinators. Palynivores are creatures that consume pollen. This article gives an insight into important topics like the structure and function of pollen.
FAQs on Pollen Grains
1. What is pollen-pistil interaction?
The interaction of pollen and pistils is a series of events that take place from the moment that pollen is deposited onto the stigma to the time when the pollen tube enters the ovule. These activities take place in chronological order. The method includes inspections at multiple points to determine whether the promotion or inhibition of pollen growth should take place. Plant breeders can use it to manipulate pollen development even in unsuitable situations. It is a precautionary measure to prevent unauthorised border crossings.
2. Explain the stages involved in the maturation of a microspore into a pollen grain?
The nucleus of each microspore mother cell undergoes meiosis or reduction division and gives rise to four haploid nuclei. This process is called microsporogenesis. The four nuclei are organised tetrahedrally and are shortly surrounded by cell walls. These are now called microspores or pollen grains. These microspores further divide once by mitosis to generate two-celled microspores to develop into a pollen grain. Each microspore The pollen grains eventually dry up and become powdery while the tapetum gets absorbed. The partition walls between the sporangia get shattered, and the microspores are freed by the dehiscence of the anther.
3. How does a pollen grain germinate?
The pollen grain lands on the stigma, which initiates pollen germination. The pollen grain's cell divides into two cells, one of which is smaller and is known as the generative cell, and the other is known as the tube cell. The intine emerges from the germ hole and forms a pollen tube. It grows into the style tissue on its way to the ovary. The tube nucleus has degenerated by this stage, and the generative nucleus has divided into two male gametes. The pollen tube opens, releasing male gametes, one of which fuses with the egg cell and the other with two polar nuclei.
