What is apomixis definition types mechanism and examples
Apomixis can be defined as a means of asexual reproduction where fertilisation. The term was first coined by botanist Hans Winkler. The seed of a plant is developed without fertilisation.
Apomixis is the process of identifying and developing diploid embryos or seeds found in a plant without fertilization or the term Apomixis can also be explained as a form of asexual reproduction that occurs via seeds, in which embryos develop without fertilization that occurs naturally in other plants.
Apomixis is also known as asexual seed formation which is obtained as the result of a plant gaining the ability to the most important process through bypassing the most fundamental and basic aspects of sexual reproduction, meiosis, and fertilization. Without the requirement for male fertilization, the resulting seed germinates a plant that develops which will be as exactly as a maternal clone.
What Are The Characteristics of Apomixis?
The characteristics of Apomixis are:
It is an asexual means of plant reproduction and is found in many species especially in fruit crops.
The process does not involve the union of male and female gametes and therefore there is no genetic recombination. Apomixis does not lead to the generation of variability in a population.
Apomixis does not permit gene flow which means it does not permit the combination of genes from different sources.
It helps in the rapid development of pure lines and can be achieved by haploid parthenogenesis.
Apomixis can be genetically controlled and is useful in conserving superior genotypes and hybrid vigor.
It has been reported in more than 300 plant species of 35 families.
Apomixis Classification
Apomixis can be classified based on:
Cell involved
Occurrence
Frequency
Apomixis Types:
Apomixis Examples:
Apomixis can be observed in hawthorns, shadbush, Sorbus, brambles, and blackberries, meadow grasses, mat grass, hawkweeds, etc.
Applications of Apomixis
Apomixis has many applications in the produce sector. Some of them are explained below:
Development of Pure Lines: Apomixis is a means of rapid production of pure lines in plants. Haploid apogamy and parthenogenesis give rise to haploid plants which after being treated by colchicine treatment can produce diploid pure lines. These pure lines can be used in the production of high yielding cultivars and hybrids.
Maintenance of Purity: Obligate apomixis breeds retain the characteristics of the mother plant which are useful in maintaining genetic purity from generation to generation. It can maintain a genotype for several generations.
Conservation of Heterosis: Obligate recurrent apomixis is useful in conserving hybrid vigor for numerous generations. As apomixis does not permit segregation, heterosis can be easily conserved.
Easy Hybrid Seed Production: Apomixis offers a simple way of hybrid seed production. These seeds are automatically produced by apomictic means and there is no need for crossing. Once a hybrid is developed using an apomictic line as one of the parents, the hybrid seed production will occur automatically. It is also more affordable than conventional methods of hybrid seed production.
Advantages of Apomixis:
Apomictic plants conserve the genetic structure of their carriers which enables them to maintain heterozygote advantages for many generations. It offers a great advantage in plant breeding where genetic uniformity is maintained for both homo and heterozygosity. The advantages of apomixis are:
Rapid multiplication of genetically uniform progenies without the risk of segregation.
Hybrid vigor or heterosis can be fixed permanently in crop plants.
If maternal characteristics are present in resultant progenies then it can be exploited from generation to generation.
The significance of Apomixis
The significance or the importance of apomixis in the plant breeding industry is massive. It is a method that develops seeds without fertilization. It can be referred to as a means of asexual reproduction which mimics sexual reproduction. It helps in the production of hybrid seeds and is cost-efficient when it comes to large-scale production. There is an increase in yield as well. Also, since there is no cross-fertilization, apomixis helps in preserving the good characteristics of a crop plant.
FAQs on Apomixis in Plants Complete Concept Guide
1. What is apomixis in plants?
Apomixis is a form of asexual reproduction in plants in which seeds are produced without fertilization. In this process, the embryo develops without the fusion of male and female gametes, meaning there is no meiosis or syngamy involved. As a result, the offspring are genetically identical to the parent plant and are often called clones. Apomixis is common in certain grasses and flowering plants.
2. How does apomixis occur in flowering plants?
Apomixis occurs when an embryo forms without fertilization in the ovule of a flowering plant. The process can occur through the following mechanisms:
- Diplospory: The embryo sac develops from a megaspore mother cell without meiosis.
- Apospory: The embryo sac develops from somatic cells of the ovule.
- Adventive embryony: The embryo arises directly from nucellar or integumentary cells.
In all cases, the resulting seed contains an embryo genetically identical to the parent plant.
3. What are the different types of apomixis?
The main types of apomixis are diplospory, apospory, and adventive embryony. They are classified as follows:
- Diplospory: Embryo sac forms from the megaspore mother cell without meiosis.
- Apospory: Embryo sac develops from somatic nucellar cells.
- Adventive embryony: Embryos arise directly from nucellus or integuments, outside the embryo sac.
These types differ in the origin of the embryo sac or embryo but all bypass normal sexual reproduction.
4. What is the difference between apomixis and sexual reproduction?
The main difference between apomixis and sexual reproduction is that apomixis occurs without fertilization, while sexual reproduction involves fusion of gametes. Key differences include:
- Apomixis: No meiosis, no fertilization, offspring are genetically identical.
- Sexual reproduction: Involves meiosis and syngamy, produces genetically varied offspring.
Thus, apomixis maintains genetic stability, whereas sexual reproduction increases genetic variation.
5. What is adventive embryony in apomixis?
Adventive embryony is a type of apomixis in which the embryo develops directly from somatic cells of the ovule such as the nucellus or integuments. In this process:
- The normal embryo sac may be present.
- Embryos arise from nucellar or integumentary cells.
- Multiple embryos may form in a single seed, a condition called polyembryony.
A common example is found in Citrus species.
6. What are some examples of apomixis in plants?
Apomixis is observed in several plant species, especially grasses and some fruit plants. Common examples include:
- Citrus (adventive embryony)
- Taraxacum (dandelion)
- Poa (bluegrass)
- Hieracium
These plants produce seeds without fertilization, ensuring uniform offspring.
7. Why is apomixis important in plant breeding?
Apomixis is important in plant breeding because it helps preserve desirable traits across generations without genetic variation. Its significance includes:
- Fixation of hybrid vigor (heterosis).
- Production of uniform crop varieties.
- Reduction in the need for repeated hybrid seed production.
If introduced into major crops, apomixis could greatly improve agricultural productivity.
8. Does apomixis involve meiosis and fertilization?
Apomixis does not involve meiosis or fertilization. In apomictic reproduction:
- Meiosis is either absent or modified.
- Fertilization (syngamy) does not occur.
- The embryo develops without fusion of gametes.
This results in seeds that are genetically identical to the parent plant.
9. What is the difference between apomixis and parthenogenesis?
The difference between apomixis and parthenogenesis is that apomixis refers to seed formation without fertilization, while parthenogenesis specifically refers to embryo development from an unfertilized egg. Key points include:
- Apomixis: A broader term involving asexual seed formation.
- Parthenogenesis: A type of apomixis where the embryo develops from an unfertilized egg cell.
Thus, parthenogenesis is one mechanism under the broader concept of apomixis.
10. What is diplospory in apomixis?
Diplospory is a type of apomixis in which the embryo sac develops from the megaspore mother cell without undergoing meiosis. In this process:
- The megaspore mother cell forms the embryo sac directly.
- Reduction division (meiosis) is absent.
- The resulting embryo is genetically identical to the parent.
Diplospory ensures clonal seed production in certain apomictic plant species.
