Why and how do plants produce pollen? An essential structure for reproduction, pollen grains are the male gametophytes of angiosperms and gymnosperms. For angiosperms, or flowering plants, pollen is produced in the anthers of their flowers. Anthers are the male reproductive structures of flowers, held up by the filaments of the flower. Together, these male reproductive parts are called the stamen. When pollen is transferred to a stigma, which is a female reproductive part of a flower, this process is referred to as pollination. Pollination is a critical step in the production of seeds, which contain the genetic material for growing the next generation of flowering plants.
Parts of a Flower
Here's a review of the parts of a flower for kids and adults who haven't studied botany recently. Flowers come in all different colors, shapes, sizes and shapes, but they all contain the same basic structures. Pollen is produced in the male parts of a flower, which are collectively called the stamen. A stamen consists of an anther and a filament, which is a long, thin structure that holds the anther up.
Together, the female reproductive parts of a flower are called the pistil. A pistil consists of a stigma, style, ovary and ovule. A stigma is the part of flower that receives pollen, and it is often a sticky knob-like structure that is designed to retain pollen that has been transferred to it.
Some flowers, called "perfect" or "complete" flowers, contain both male and female parts. Others have separate male and female flowers on the same plant; these are called monoecious. In some plants, male and female flowers are on different plants; these plants are referred to as dioecious.
Production of Pollen
Regardless of whether a plant species is monoecious, dioecious or produces perfect flowers, all flowering plants make pollen. Produced in the anthers of a flowering plant, pollen is usually powdery and fine, the perfect package for easy transfer. Pollen particles are often referred to as grains, and there are as many shapes, sizes and colors of pollen as there are flowers.
Wind-pollinated plants usually produce abundant quantities of lightweight, smooth pollen grains that are picked up easily by the slightest breeze. Plants that are assisted by pollinators like bees and moths often produce smaller quantities of heavy, sticky pollen grains that attach themselves to insects when they come to feed on nectar and collect pollen to eat.
Plants are characterized by the alternation of generations, and pollen is the haploid phase of flowering plants. Also called the gametophyte stage, pollen is made by mother cells in the anthers of a flower. In diploid plants, the first step is the meiosis of pollen mother cells. After this, the unicellular products of the meiosis of mother cells, which are called microspores, divide through mitosis.
The bicellular pollen grain produced by mitosis undergoes further transformation to prepare it for pollinating and fertilizing a female ovule. At the end of this process of pollen production, the result is a pollen grain made up of three cells. This pollen grain is composed of one cell that will become a pollen tube and two sperm cells.
Pollinators and Pollination
As mentioned, the pollen of some plants is moved easily by wind. Wind-pollinated plants usually have adaptations that help this process along, such as long stamens and pistils that extend out of their flowers, increasing the chances of transfer of pollen from anthers to stigmas.
Many plants depend on the help of pollinators like bumble bees and hummingbirds to move their pollen from male flower parts to female flower parts. In fact, insects assist with about 80 percent of plant pollination, according to some estimates. Most plant-pollinator relationships are mutualistic, as both the plants and pollinators benefit from working together.
Whether pollen is moved by an insect or the wind, the end game is the same: pollination. After pollination, a pollen grain grows a tube to move down the plant pistil to fertilize the female ovule, and successful plant fertilization results in the production of the next generation of the plant species, represented by seeds that develop within the female structures of the plant.
About the Author
Meg Schader is a freelance writer and copyeditor. She holds a Bachelor of Science in agriculture from Cornell University and a Master of Professional Studies in environmental studies from SUNY College of Environmental Science and Forestry. Along with freelancing, she also runs a small farm with her family in Central New York.