In a species showing sporophytic incompatibility, which type(s) of pollen could successfully fertilize an S₂ S₃ flower?
a. S₁ pollen from an S₁ S₃ flower
b. S₂ or S₃ pollen from an S₂ S₃ flower
c. S₃ pollen from an S₁ S₁ flower
d. S₁ pollen from an S₁ S₁ flower

Verified step by step guidance

1. Understand the concept of sporophytic incompatibility: In sporophytic incompatibility, the ability of pollen to fertilize a flower is determined by the genotype of the pollen-producing plant, not the pollen itself. The incompatibility is controlled by the S-locus, which has multiple alleles.
2. Identify the genotype of the flower: The flower in question has the genotype S2S3. This means it will reject pollen from plants that have either S2 or S3 alleles in their genotype.
3. Analyze option (A): S1 pollen from an S1S3 flower. The pollen-producing plant has the genotype S1S3. Since the flower has S2S3, it will reject pollen from any plant with S3 allele, making this option incompatible.
4. Analyze option (B): S2 or S3 pollen from an S2S3 flower. The pollen-producing plant has the genotype S2S3. Since the flower has the same alleles, it will reject pollen from this plant, making this option incompatible.
5. Analyze option (C) and (D): S3 pollen from an S1S1 flower and S1 pollen from an S1S1 flower. The pollen-producing plant has the genotype S1S1. Since the flower has S2S3, it will accept pollen from a plant with no S2 or S3 alleles, making these options potentially compatible.

Key Concepts

Sporophytic Incompatibility

Sporophytic incompatibility is a mechanism in plants that prevents self-fertilization and promotes genetic diversity. It is controlled by the genotype of the sporophyte (the parent plant) rather than the pollen itself. In this system, the pollen's ability to fertilize is determined by the alleles present in the parent plant's sporophyte tissue, and pollen carrying the same alleles as the stigma will be rejected.

Genotype and Alleles

Genotype refers to the genetic makeup of an organism, specifically the alleles it possesses. Alleles are different forms of a gene that can exist at a specific locus. In the context of sporophytic incompatibility, the genotype of the flower (e.g., S2S3) determines which pollen can successfully fertilize it, as pollen with matching alleles to the stigma's genotype will be incompatible.

Pollen-Stigma Interaction

Pollen-stigma interaction is a critical process in plant reproduction where pollen lands on the stigma and begins the fertilization process. In sporophytic incompatibility, this interaction is influenced by the genetic makeup of the pollen and the stigma. Successful fertilization occurs when the pollen's alleles do not match those of the stigma, allowing the pollen tube to grow and fertilize the ovule.