Due to our nature, it is easy for us to imagine how animals reproduce, since their fertilization process is generally similar to ours. However, it takes a little longer to find these similarities with the plant world. As they do? What is plant fertilization?
The purpose of this article is to explain what plant fertilization is. For this we will talk about the two large groups that exist: Angiosperms and gymnosperms. So do not hesitate to continue reading if you are interested in the subject and want to know more about plant fertilization.
Before explaining plant fertilization, we will first comment on what the concept of fertilization is. It is the process by which Two gametes, male and female, fuse during reproduction. In this way, a zygote is created which contains a genome, a product of the parents.
In the plant world, Pollination takes place first. The male reproductive leaves generate pollen grains which are carried by insects or by the wind to the stigmas. This is where they germinate. When we talk about plants, we are usually not talking about gametes, but spores. Each pollen grain usually contains two male reproductive cells, or gametes. However, there are different methods used by plants, since not all species are the same, in fact, they differ a bit when it comes to reproduction.
How to tell if a plant is male or female
As you well know, plants can be differentiated in many ways. There are a large number of groups, classes and types of vegetables and each species belongs to several. However, there are two major groups that differ in their mode of reproduction. So, There are vegetables with flowers and those without flowers. The former are known as angiosperms and are the most abundant plants on this planet. Moreover, these two types of vegetables are the newest. Instead, plants without flowers are part of the gymnosperm group. They are the first to appear on Earth, even before the dinosaurs.
Among the angiosperms, there are various plants such as shrubs, trees, azaleas, dimorphoteca, etc. Regarding gymnosperms, these are mainly composed of conifers. Some examples for this group would be cedars, yews, pines. Cycads also belong to gymnosperm plants. But don’t worry, we will talk in more detail about the two types of plants, their structures and the course of fertilization.
Let’s start with the gymnosperms. While it is true that these plants are notorious for not having flowers, they do, but not the typical ones we imagine. Its flowers have neither sepals nor petals, but the females form a kind of woody, greenish cone that eventually becomes false fruits, like pine cones.
Plants belonging to this group have both male and female flowers. The latter has a scale, two ovules and a bract which form the female cone by grouping just around a floral axis. Each egg contains an embryo sac with two archegonia inside. which, in turn, have two female gametes or oospheres each. Let’s clarify these concepts:
- Archegonia: It is the female reproductive organ of fungi, algae and bryophytes, such as mosses and some vascular plants such as ferns. It is completed by the male organ called the antheridium.
- Oospheres: It is the female gamete of plants. They arise from the so-called megaspore through a process called megagametogenesis. At a basic level, we can say that it is the mitotic divisions. During double fertilization, the oospheres fuse with the generative nuclei of the pollen grain and thus give rise to the embryo.
As for the male flowers, they form male cones around a floral axis. They have a scale and also two microsporangia or pollen sacs in which they end up forming the mother cells which in turn give rise to the famous pollen grains. Inside, there are totally two male gametes, also called antherozoids. They also contain two air sacs which aid in dispersal until they reach the female flower. In this case, I think it will also be good to explain some concepts:
- Microsporangia: These are structures that also produce and contain spores. They are basically microscopic bodies whose purpose is to disperse and survive for a long time.
- Antherozoids: It is essentially the male gamete, which would be equivalent to our sperm.
Fertilization of gymnosperm plants
Knowing a little about the structures of the male and female flowers of gymnosperms, we will now comment on the functioning of this fertilization. Note that the pollen grain can take up to a year to germinate, once the female flower has been reached. When this happens, the pollen tube opens very slowly through the so-called nucellus of the egg cell. When it reaches the female gametophyte, its next task is to cross the neck of the archegonium and then enter the oosphere. where you upload all your content. It is at this time that the fertilization of gymnosperm plants takes place.
Angiosperms and gymnosperms
During this process, one of the gametes ends up uniting with the nucleus of the oosphere in which it takes place. As a result, the zygote is formed, which is a cell from which the embryo is formed and develops. Concerning the vegetative nucleus, the other cells of the archegonium and the other male gamete, all degenerate. During this time, the endosperm, consisting of reserve cells, surrounds the embryo, which is protected by the integument of the ovum, which in turn lignifies. The embryo is considered fully mature when the seeds are released. This process can easily take two years from the time the flowers appear.
In the case of pine seeds, the seed coat is diploid and is produced by the maternal sporophyte. As regards the primary endosperm or reserve tissue, this is haploid since it is part of the female gametophyte. After fertilization, a diploid embryo is formed, which is the new sporophyte.
We already know what gymnosperms are and how they work, but what about angiosperms? Before explaining the fertilization of these plants, We must first clarify some concepts To better understand the process:
- carpels: They are modified leaves which, in their entirety, form the female reproductive part of the flower of angiosperm plants. The set of all the carpels of a flower is called a gynoecium.
- Stigma: It is the part of the gynoecium that receives pollen during pollination.
- Micropyle: Also known as micropyle, it is a hole or opening that is found in the apical part of the seminal rudiments or ovules.
- Synergists: These are cells whose nucleus is at the end of the embryo sac of angiosperm plants. Each embryo sac contains two. The two synergids together form the filiform or filarial apparatus. It should be noted that they help the oosphere during the fertilization process.
- polar nuclei: These nuclei are cells present inside the embryo sac, female gametophyte or ovary. They are involved in the fertilization of plants.
It must be said that each embryo sac has different types of cells, including the fertile ones are the polar nuclei and the ovum. However, the steriles, which would be the antipodals and the synergists, also collaborate during the fertilization process.
fertilization of angiosperm plants
To finish on the subject of fertilization in plants, we will talk about the functioning of angiosperms. Once the carpel has been pollinated, the sugary liquid, composed mainly of sucrose and generated by the mature stigma, stimulates the germination of the pollen grain. From each of these grains emerges a pollen tube whose purpose is to create a path through the style until it reaches the female gametophyte or embryo sac of angiosperm plants. This embryo sac is located inside the egg.
What are angiosperm plants?
The male gametes or generative nuclei travel through the pollen tube until they reach the micropyle. The pollen tube passes through this structure and discharges all its contents into the embryo sac, close to one of the two synergids. After this process, the generative nuclei fuse with both the oosphere and the polar nuclei, which is why it is called “double fertilization”.
There are many pollen grains which usually reach the stigma and hence germinate. However, only one of them will produce fertilization. Once the ovary is fertilized, it begins to turn into a fruit. In these fruits which have several seeds, there are also several grains of pollen necessary for them to fuse with each of the ovules.
It’s funny how nature has arranged everything so that different types of vegetables can reproduce, isn’t it? Undoubtedly, this land is full of amazing creative and breeding abilities.