Self incompatibility: Definition, Meaning, Formation, Types, Functions, Characteristics

Definition of Self Incompatibility

Self-incompatibility in flowering plants is a genetic process to prevents self-fertilisation and favours 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 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.

Basics Of Plant Reproduction

Sexual reproduction of plants involves the fusion of male and female gametes to form seeds that grow into new plants.

Overview Of Sexual Reproduction In Plants

Generally, this is a result of pollination, wherein pollen from the male part of the flower is transferred to the stigma, which is the female part. Hence, fertilisation takes place, followed by development into seeds in the ovary.

Self-Pollination Vs. Cross-Pollination

Self-pollination is a process by which another produces pollen and transfers it to the same flower or another flower on the same plant. On the other hand, the transfer of pollen from the anther of one plant onto the stigma of another plant is cross-pollination. Cross-pollination ensures variability while self-pollination results in inbreeding.

What Is Self-Incompatibility?

SI is a genetic mechanism in flowering plants that prevents self-fertilisation but allows for the possibility of cross-pollination.

SI means that it achieves genetic diversity by rejecting pollen from the same plant or similar individuals. This ensures healthy populations of plants, avoiding inbreeding.

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 reproductive biology of plants.

Types Of Self Incompatibility

In gametophytic self-incompatibility, pollen compatibility would be based on its haploid genotype

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 of Plants with GSI

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 and the stigma determine the compatibility. If the pollen is identified as 'self', it is inhibited from germinating or penetrating the stigma.

Examples of Plants with SSI

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.

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