The key difference between gametophytic and sporophytic self incompatibility is that in gametophytic self-incompatibility system, pollen phenotype is determined by its gametophytic haploid genotype while in sporophytic self-incompatibility, pollen phenotype is determined by the diploid genotype of the plant.
Self-incompatibility is a pollination control mechanism in plants. It primarily prevents self-pollination and enforces cross-pollination, which is an evolutionary advantageous. Self-incompatibility occurs as a result of negative chemical interactions between pollen and style tissue within the same allele. Although pollens and pistils are viable and fertile, pollen germination does not take place in these plants. When pollen germination does not happen, the pollen tube cannot form. Then the pollens fail to deliver male gametes into female gametes for fertilization. As a result, they cannot produce seeds.
There are two major self-incompatibility systems as gametophytic self-incompatibility and sporophytic self-incompatibility. They are single locus self-incompatibility systems that are based on a single multi-allelic locus (S). This locus consists of one pistil expressing S gene and one pollen expressing S gene.
CONTENTS
1. Overview and Key Difference
2. What is Gametophytic Self Incompatibility
3. What is Sporophytic Self Incompatibility
4. Similarities Between Gametophytic and Sporophytic Self Incompatibility
5. Side by Side Comparison – Gametophytic vs Sporophytic Self Incompatibility in Tabular Form
6. Summary
What is Gametophytic Self Incompatibility?
Gametophytic self-incompatibility is a type of self-incompatibility in which the S phenotype of the pollen is determined by its own haploid S genotype. It requires strict codominance between S alleles in the pistil to prevent heterozygous individuals from becoming compatible with their own pollens. Generally, a pollen parent with S1 and S2 genetic constitution produce gametes of S1 and S2. In a female parent, same alleles S1 and S2 are codominant and get expressed. Therefore, when pollen grains with S1 and S2 fall on a plant with S1 and S2, both pollens will not germinate since the reaction in stigma is codominance. If S1 and S2 pollens fall on S1 and S3 plant, S2 pollen can germinate due to partial incompatibility. Moreover, if S1 and S2 pollens fall on S3 and S4, both pollens can germinate since it is completely compatible.
Figure 01: Gametophytic Self Incompatibility
Strict codominance is very important in gametophytic self-incompatibility. Pollen grains having different alleles to style tissue will germinate while other pollens will not germinate. Moreover, gametophytic self-incompatibility is more common than sporophytic self-incompatibility. But, it is less well understood.
What is Sporophytic Self Incompatibility?
Sporophytic self-incompatibility is a self-incompatibility system in which the pollen S phenotype is determined by the diploid S genotype of its parent plant. In the sporophytic self-incompatibility system, the genotype of the sporophyte (parent plant) determines the incompatibility reaction and S1>S2, S2>S3 and S3>S4, etc.
Figure 02: Sporophytic Self Incompatibility
Male gametes of both S1 and S2 behave as S1. Similarly, in the style, S1 and S2 behave as S1. Hence, the fusion between them is incompatible. Similarly, the cross between S1S2 and S1S3 is also incompatible. But, a cross between S1S2 and S3S4 is compatible. Sporophytic self-incompatibility is commonly seen among the members of family Brassicaceae.
What are the Similarities Between Gametophytic and Sporophytic Self Incompatibility?
- Gametophytic and sporophytic self-incompatibility are two types of self-incompatibility systems.
- Both mechanisms prevent self pollination and promote cross-pollination.
- Both mechanisms are evolutionarily advantageous.
- They are single locus self-incompatibility systems.
- Moreover, they are tightly controlled genetic systems.
What is the Difference Between Gametophytic and Sporophytic Self Incompatibility?
Self-incompatibility is a mechanism that prevents pollens from one flower fertilizing other flowers of the same plant (self pollination). Gametophytic self-incompatibility occurs if the pollen genotype is the same as the female genotype. Therefore, gametophytic self-incompatibility is determined by the genotype of haploid pollens. In contrast, sporophytic self-incompatibility is determined by the diploid genotype of the sporophyte generation. Sporophytic self-incompatibility occurs when the pollens contain either of the two alleles in the sporophyte parent. So, this is the key difference between gametophytic and sporophytic self incompatibility.
Below infographic shows more details of the difference between gametophytic and sporophytic self incompatibility.
Summary – Gametophytic vs Sporophytic Self Incompatibility
Self-incompatibility is one of the major mechanisms that promote cross-pollination. It prevents the fusion of fertile male and female gametes of the same flower or the same plant. Moreover, self incompatibility plays a significant role in hybrid seed production. Gametophytic self incompatibility is determined by the genotype of gametes while sporophytic self incompatibility is determined by the genotype of the plant. Thus, this is the key difference between gametophytic and sporophytic self incompatibility.
Reference:
1. Narayanapur, V., Suma, B., & Minimol, J. (2018). Self-incompatibility: a pollination control mechanism in plants. INTERNATIONAL JOURNAL OF PLANT SCIENCES, 13(1), 201-212. doi: 10.15740/has/ijps/13.1/201-212
Image Courtesy:
1. “Gametophytic self-incompatibility” (CC BY-SA 3.0) via Commons Wikimedia
2. “Sporophytic self-incompatibility” (CC BY-SA 3.0) via Commons Wikimedia