Self incompatibility: Definition, Meaning, Formation, Types, Functions, Characteristics
Self-incompatibility (SI) is a genetic mechanism in flowering plants that prevents self-fertilisation and promotes cross-pollination. The definition of self-incompatibility explains how plants avoid inbreeding and maintain genetic diversity. It enables plants to distinguish between “self” and “non-self” pollen using S-genes, ensuring greater genetic diversity and healthier populations. SI is a high-yield NEET concept linking reproduction, genetics, and pollination biology.
This Story also Contains
- Definition of Self-Incompatibility and Its Significance
- Characteristics of Self-Incompatibility
- Types of Self-Incompatibility
- Self-incompatibility S-Genes and Molecular Mechanism
- Self-Incompatibility vs Self-Pollination
- Self-Incompatibility Importance in Plant Breeding
- Disadvantages of Self-Incompatibility
- Self-Incompatibility NEET MCQs (With Answers & Explanations)
- Recommended video on "Self Incompatibility"
The formation of self-incompatibility occurs when pollen from the same plant fails to fertilise the ovule. This mechanism is controlled by specific genes and biochemical reactions. Self-incompatibility types include gametophytic and sporophytic systems. It plays a major role in sexual reproduction in flowering plants, confirming cross-pollination and variation. Functions of self-incompatibility maintain adaptability in plant populations, with examples like Brassica and Petunia important for exams.
Definition of Self-Incompatibility and Its Significance
Self-incompatibility in flowering plants is a genetic process to prevent self-fertilisation and promote cross-pollination. It allows a plant to recognise and reject its pollen or pollen from individuals that are similar genetically. In such a way, this provides the certainty that only pollen from different plants will fertilise the ovules. This is a complex interaction at the surface of the pistil between pollen and the surface of the pistil, controlled by special genes often called S-genes.
Self-incompatibility is, therefore, of fundamental value to the gene diversity of plant populations, and a low degree of it equates to reduced adaptability and survival in the long term. Through the process of preventing inbreeding, this process reduces the chances of the occurrence of genetic defects and enhances the chances of the introduction of new variations. There has to be such a mechanism for the evolution of plant species for better survival in changing environments.
Historical Background And Discovery
The phenomenon of self-incompatibility was first discovered in the early 20th century by scientists working on plant breeding. Since then, research into SI mechanisms has outlined several molecular and genetic procedures that plants use to recognise and reject their pollen, thus contributing to our general understanding of the reproduction in plants.
Characteristics of Self-Incompatibility
Self-incompatibility is a process in flowering plants that stops self-pollination and allows cross-pollination. It works through signals between the pollen and the stigma of the flower that decide whether fertilisation will happen. This process helps plants maintain variation and strength in their populations.
- Self-incompatibility stops pollen from the same plant from fertilising the ovule. This avoids inbreeding and keeps the plant population healthy.
- It allows fertilisation only with pollen from another plant, which increases diversity.
- Pollen proteins interact with stigma receptors. These signals decide whether pollen is accepted or rejected.
- Gametophytic self-incompatibility and sporophytic self-incompatibility are the two systems found in plants.
- Examples include Petunia, Tobacco, Brassica, and members of Asteraceae. These plants rely on self-incompatibility to maintain variation.
Types of Self-Incompatibility
Self-incompatibility in plants is of two major types based on the genetic control of pollen–stigma interaction. These mechanisms prevent self-fertilisation and promote cross-pollination, ensuring genetic diversity in sexual reproduction in flowering plants.
Gametophytic Self Incompatibility (GSI)
If the genotype of the pollen is the same as the genotype of the stigma, it is recognised as self and rejected. Thus, blocking fertilisation. This involves specific interacting proteins which trigger pollen tube inhibition
Examples:
Gametophytic self-incompatibility is found in plants such as petunias, tobacco, and some grasses - all of which rely on this mechanism to ensure cross-pollination for genetic diversity.
Sporophytic Self Incompatibility (SSI)
Sporophytic self-incompatibility is dependent on the diploid genotype of the parent plant producing the pollen. The interaction takes place at the surface of the stigma, where proteins from the pollen structure and the stigma determine the compatibility. If the pollen is identified as 'self', it is inhibited from germinating or penetrating the stigma.
Examples:
Sporophytic self-incompatibility is seen in Brassica species (which include cabbage and mustard) as well as some Asteraceae members. This ensures that there is genetic diversity in populations of these plants.
Self-incompatibility S-Genes and Molecular Mechanism
Self-incompatibility is controlled by S-genes located at the S-locus. These genes regulate the recognition system between pollen and stigma, ensuring that self‑pollen is rejected. The process is a classic example of pollen-pistil interaction, where molecular signals decide compatibility. The components of the S-locus and the molecular mechanism are:
Pollen S-gene: The pollen S-gene encodes a specific S-protein carried by the pollen grain, which acts to signal its genetic “self” to the stigma.
Stigma S-gene: The stigma expresses its own S-protein receptor that can recognise incoming pollen S-proteins and determine whether they match the plant’s self-identity.
Interaction: When the pollen S-protein matches the stigma’s S-receptor, the system triggers a rejection response, preventing fertilisation. If they do not match, pollen is accepted, and fertilisation can proceed.
Self-Incompatibility vs Self-Pollination
Self-incompatibility is a genetic mechanism in plants that prevents self-fertilisation and promotes cross-pollination. Self-pollination allows fertilisation within the same flower, leading to low genetic variation. The difference between self-incompatibility and self-pollination explains how plants control reproduction.
The difference between self-incompatibility and self-pollination is:
Feature | Self-incompatibility | Self-pollination |
Outcome | Rejection of own pollen | Acceptance of one's own pollen |
Genetic variation | High | Low |
Pollination type | Cross pollination | Selfing possible |
Controlled by | S-genes | No special genes |
Self-Incompatibility Importance in Plant Breeding
The advantages of self-incompatibility are:
Promotes outbreeding: Ensures pollen from genetically different individuals fertilises the plant, which increases genetic diversity.
Maintains genetic diversity: Helps preserve a wide range of alleles in a population.
Prevents inbreeding: Reduces the chances of harmful recessive traits expressed during close relative mating.
Supports plant adaptations: Provides genetic diversity that improves the ability of a plant to adapt in an environment.
Encourage hybrid: Favours cross-pollination that can produce stronger, more resilient offspring.
Disadvantages of Self-Incompatibility
The disadvantages of self-incompatibility are very few and mostly rare. Some of the disadvantages include:
In self-incompatible plants, the ability to self-fertilise means that a shortage of pollinators can lead to poor or no pollination.
When plants grow far from compatible mates, self-incompatibility restricts reproduction, resulting in few or no seeds.
Self-Incompatibility NEET MCQs (With Answers & Explanations)
Important topics for NEET are:
Types of Self-incompatibility
S-genes and their molecular mechanism
Advantages of Self-incompatibility
Practice Questions for NEET
Q1. What are the genetic mechanisms that regulate self-incompatibility in plants?
Gametophytic and sporophytic
Heterozygotic and homozygotic
Dominant and recessive
Polygenic and monogenic
Correct answer: 1) Gametophytic and sporophytic
Explanation:
Self-incompatibility in plants is regulated by two main genetic mechanisms: gametophytic and sporophytic.
Gametophytic self-incompatibility involves the interaction between the pollen and the stigma. The S-allele gene is expressed in the pollen, and the S-receptor gene is expressed in the stigma. If the pollen and stigma express the same S-allele, the pollen will not be able to fertilize the ovules.
In sporophytic self-incompatibility, the interaction occurs between the pollen and the maternal tissues of the plant. The S-allele gene is expressed in the sporophyte, and the S-receptor gene is expressed in the stigma. If the pollen and sporophyte express the same S-allele, the pollen will not be able to fertilise the ovules.
Overall, these mechanisms ensure that plants cannot self-fertilise, promoting genetic diversity within the species.
Hence, the correct answer is option 1) Gametophytic and sporophytic.
Q2. Which of the following is not true about the mechanism to control inbreeding depression?
Pollen release & stigma receptivity are synchronised.
Anther & stigma are placed at different positions.
Self incompatibility
Production of unisexual flowers
Correct answer: 1) Pollen release & stigma receptivity are synchronised.
Explanation:
If both male and female flowers are present on the same plant, such as castor and maize (monoecious), it prevents autogamy but not geitonogamy. In several species, such as papaya, male and female flowers are present on different plants; that is, each plant is either male or female (dioecy). This condition prevents both autogamy and geitonogamy.
Inbreeding depression can be controlled by preventing the fusion of gametes of the same plant.
Mechanisms to control inbreeding depression
1. Pollen release and stigma receptivity are not synchronised
2. The anther and stigma are placed at different positions so that the pollen cannot come in contact with the stigma of the same flower
3. Self-incompatibility
4. Production of unisexual flowers
Hence, the correct answer is option 1) Pollen release & stigma receptively are synchronised.
Q3. Self-incompatibility in plants is a genetic mechanism that promotes:
Self-pollination
Cross-pollination
Inbreeding
Vegetative propagation
Correct answer: 2) Cross-pollination
Explanation:
Self-incompatibility in plants is a genetic mechanism that prevents self-pollination and promotes cross-pollination. It is a well-designed mechanism by which certain plants recognise and reject their pollen, thus encouraging outbreeding. This mechanism ensures genetic diversity in plant populations by promoting the transfer of pollen from one plant to another, typically through the assistance of pollinators like insects, birds, or wind. Self-incompatibility helps to prevent inbreeding and maintain genetic variability within plant species, leading to healthier and more adaptable populations.
Hence, the correct answer is option 2) Cross-pollination.
Recommended video on "Self Incompatibility"
Frequently Asked Questions (FAQs)
It works through pollen‑stigma signals controlled by S‑genes, where matching pollen is rejected and non‑matching pollen is accepted.
Examples include Petunia, Tobacco, Brassica (cabbage, mustard), and members of Asteraceae.
Self-incompatibility avoids self-fertilisation and promotes cross-pollination, a process that enhances genetic variation and reduces the risk of inbreeding in plant populations.
