Flowering plants follow three reproductive systems:
- special methods – apomixis (asexual production)
Apomixis occurs in more than 35 plant families, including grains such as corn and wheat. The word ‘apomixis’ has a Greek origin – ‘APO’ means “away from” and ‘MIXIS’ means “act of mixing or blending”. Antonie van Leeuwenhoek discovered the phenomenon of apomixis in orange seed in 1719.
Special mode- apomixis involves the formation of seeds without fertilization. Genetic reunification is not found in apomixis as there is no mixing between male and female gametes. This procedure appears to be effective in maintaining a hybrid seed as there is no meiosis involved. Apomixis is a relatively inexpensive and time-efficient seed production process that assists farmers to plant hybrid seeds. In addition, it may seem commercially viable as high-end features can be passed on to new generations.
Special methods – Definition of apomixis
Apomixis in plants refers to the reproductive process that occurs in a seed, in which embryos develop without fertilization. That means the reproductive organs of related structures are involved, but no zygote is formed by gametic integration. Therefore, Apomixis is a special breed of asexual reproduction that replaces normal reproduction. The resulting embryo, including a baby plant, resembles its mother’s genetic code. In addition, these plants are virtually free of harmful bacteria.
Certain types of plants may produce embryos without fertilization of eggs and pollen. This condition is called apomixis in plants, and the seedlings produced by this process are known as ‘apomicts’. The term, ‘apomixis’ was coined by botanist Hans Winkler in 1908, as a special form of asexual reproduction ‘without fertilization’. It should be noted that the normal production of asexual plants, such as dispersal from leaves, cannot be considered apomixis. However, replacing plants or replacing bulbil with flowers is considered apomixis.
- Apomixis is an asexual method of reproduction in plants. This condition occurs in more than 300 plant species of 35 families.
- This process does not involve the integration of male and female gametes; thus, there is no regeneration of genes.
- It helps to develop pure offspring, which can be achieved through haploid parthenogenesis. Haploid parthenogenesis is a rare form of parthenogenesis that occurs in a few species of bees, nematodes, and plants – the offspring grow in haploid eggs to produce adult haploids.
- Apomixis can be genetically modified, making it useful for maintaining high genes.
Special methods – Editing Apomixis
Depending on the cell involved, the occurrence, and the frequency, Apomixis is divided into four groups.
- Repeated apomixis or Gametophytic apomixis
In this apomixis, the embryonic stem grows without meiosis from diploid cells. The deployed cell has paired chromosomes. Both egg and fetus are diploid. Thus, this new egg has a normal number of chromosomes the size of a mother plant. The embryo evacuates from the egg nucleus without fertilization. Examples of plant species are ‘Crrepis’ and ‘Allium’.
- Non-recurring apomixis
In the recurrent apomixis, the embryo develops directly into the egg cell of the haploid sac or other haploid cells without fertilization. The haploid cell has a single set of organic chromosomes. Therefore, the embryonic embryo is also haploid and infertile. This type of apomixis is uncommon in plant species and is highly dependent on genetic interest. Examples of plant species are ‘Solanum nigrum’ and ‘Lilium’.
- Adventitious embryonic
Also known as sporophytic budding or nucellar embryonic. It is a type of sporophytic apomixis. The embryo grows directly from a nucellus or a group of nucellus cells or integuments, leading to the formation of a shoot-like structure. The resulting embryonic stem cells are diploid just as the nucleus cells are diploid. Nucellar embryonic usually occurs in tropical and subtropical climates, including citrus and mango.
- Vegetative apomixis or bulbils
In this type of apomixis, vegetative buds are called bulbils that grow instead of flowers. These bulbs are easy to produce and may grow into new plants while attached to the mother plants. This type of apomixis is most common in ‘Allum’, ‘Poa’, ‘Bulbosa,’ and other grasses.
Typical examples of Apomixis
Apomixis occurs most commonly in sweet oranges, grapes, lemons, dandelions, hawthorn, blackberries, meadow grasses, and hawkweed.
Benefits of Apomixis
Apomictic plants inherit the genes of their mother plants, enabling them to maintain genetic similarity for many generations. The main advantages of apomixis are as follows:
- Guaranteed production in high-risk areas as foreign pollen does not contribute to production.
- It helps to produce hybrid seeds of apomictic plants.
- It is very expensive for seed production.
- Apomixis prevents the loss of certain hybrid features.
- Apomixis can be genetically engineered to maintain high genotypes and hybrid traits.
The main disadvantages of special-apomixis methods are as follows:
- It cannot control the growth of harmful genetic mutations.
- This practice usually occurs in small natural areas. The process cannot adapt to rapid changes in locations.
The importance of apomixis in plant reproduction
Special methods of apomixis have been shown to be beneficial in the plant breeding industry. This method helps to improve the seed without adding fertilizer. Since there is no meiosis during seed formation, high seed characteristics remain the same. These positive traits are passed on to the next generation, thus maintaining the hygiene of the hybrid seed.
Hybrid seeds are expensive to plant. However, special modes-apomixis help farmers to grow crops all year round without having to buy hybrid seeds. Therefore, the apomixis process proves to be costly for farmers.
Apomixis is also a time-saving process. Hybrid seeds allow farmers to plant crops every year because they give a higher yield in a shorter time.
Is apomixis possible in animals?
In all production methods, specialized methods - apomixis and polyembryony are very common in both plants and animals. In animals, apomixis occurs when a young person grows into an unfertilized egg.
What are the similarities between apomixis and parthenocarpy?
Among the asexual methods of reproduction, the special methods-apomixis and parthenocarpy are remarkably similar. In either case, fertilization is not involved. In addition, they both use the genitals of plants.
What is the difference between facultative and obligate apomixis in plants?
Sexual reproduction is suppressed or absent from a variety of apomictic plants. Facultative apomixis means that apomixis does not always happen and that sexual intercourse also occurs. On the other hand, when sexual reproduction is completely suppressed or absent, it is called apomixis bound to plants.