Plants have a large number of propagation and reproduction mechanisms to ensure their survival and colonize new territories, something that is not in vain because they have been here much longer than we have.
Among the many forms of multiplication available to them, one of them allows them to produce seeds asexually, that is, without needing another plant to fertilize the ovules. How is it possible that reproduction by seeds, the method of sexual reproduction, occurs precisely asexually? Thanks to apomixis. If you want to learn more about this reproductive mechanism, keep reading us in this AgroCorrn article about what apomixis is, its types and examples .
What is apomixis
The definition of apomixis says that it is a reproductive mechanism that allows the plant to clone itself through its seeds , instead of producing them sexually as usual. It is, therefore, a form of asexual reproduction by production of apomictic seeds .
Like other forms of asexual reproduction , it is characterized by offering the plants that use it greater ease of propagation and colonization in exchange for sacrificing genetic variability and the adaptability that it provides from an evolutionary point of view . Thus, it is an ideal mechanism for the survival of the species in environments to which it is already adapted, simply providing a greater presence.
Apomixis occurs without the presence of meiosis , that is, without the embryo being formed from fertilization and generation of viable endosperm. Apomictic seeds are formed solely from the maternal ovum and, therefore, are genetically the same as the mother plant . It is a very common mechanism in many families and genders, as we will see later.
We also recommend you read more about asexual reproduction in plants: what it is, characteristics, types and examples in this other post.
Types of apomixis
Three types of apomixis mechanisms are known :
In diplosporia, also known as diploid parthenogenesis, the embryo arises from a non-reduced embryo sac, so the new individual has the same chromosome number as the parent plant. This type of apomixis occurs when the female gametophyte forms directly from the embryo. In diplosporia, there is always the presence of a diploid embryo.
Aplosporia is a type of asexual reproduction in which the somatic cells give rise to the embryo sac. This arises specifically from a somatic cell located in the nucela around its mother cell. Here a gametophyte appears, but not by meiosis, so the embryo is diploid as well. The chromosome number is also not reduced in aposporia.
Adventitious embryo, also called sporophytic apomixis or nucellar embryo, is a very common type of apomixis in fruit trees, specifically in citrus. In this type of apomixis there is no appearance of an embryo sac, since the embryo arises from a diploid sporophyte, without meiosis or the appearance of a female gametophyte.
Examples of apomixis
The first example of apomixis, which coincides precisely with the appearance of the term, occurred in 1841, when the Kew botanical gardens, in London, welcomed a specimen from Australia, Alchornea ilicifolia . It was a female plant that, when isolated, produced flowers and, to the surprise of those in charge of the botanical garden, a large quantity of seeds. It was thus clear that, without viable pollination options, the plant had produced seeds in a totally asexual way, thus being recognized as the first documented case of apomixis.
Soon after, Gregor Mendel, when experimenting with some Hiracium species, would lead to the first inadvertent case of experimentation with apomixis, in a process that he himself erroneously called self-pollination.
Another of the most common examples of apomixis is that of the dandelion , with the scientific name Taraxacum officinalis . This plant frequently resorts to apomixis cloning to multiply, spreading its seeds with its characteristic ability to be blown away by the wind. The dandelionscapable of resorting to apomixis, they also enjoy a greater geographic distribution than those species that cannot, thus demonstrating the success of this asexual reproduction mechanism under the appropriate conditions. Of course, even the species of dandelions that habitually use apomixis occasionally resort to sexual reproduction, even hybridizing, and it is seldom advisable to completely close off genetic variability and their adaptive capacities.
We also find cases of apomixis in practically all the species of the Poaceae family, the so-called grasses , a family of great economic importance for humans, with more than 800 genera and 12,000 described species. In fact, in this area specifically, it is studying how to take advantage of apomixis in crops of grass plants as vital as corn and wheat, since it would allow to easily improve the quantity and quality of production.
Other genera in which this asexual reproduction mechanism is commonly found are Asteraceae, Rosaceae and Rutaceae, plants that surround us in a very common way and with a great distribution.
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