Module: | Pollination & Outbreeding Devices
Q56: Consider the following statements regarding the physiological mechanisms of self-incompatibility:
1. Self-incompatibility is a genetically controlled mechanism that relies on multiple alleles to recognize and reject self-pollen.
2. In some species, if the incompatibility reaction occurs on the stigma, the self-pollen grain fails to germinate entirely.
3. If the incompatibility reaction occurs in the style, the pollen tube successfully reaches the ovule but is physically blocked from entering the micropyle.
Which of the above statements is/are correct?
2. In some species, if the incompatibility reaction occurs on the stigma, the self-pollen grain fails to germinate entirely.
3. If the incompatibility reaction occurs in the style, the pollen tube successfully reaches the ovule but is physically blocked from entering the micropyle.
Which of the above statements is/are correct?
✅ Correct Answer: A
The correct option is A. Statements 1 and 2 are correct, but Statement 3 is incorrect.
Self-incompatibility (SI) is the ultimate genetic barrier against inbreeding.
It operates via an S-locus with multiple alleles; if the alleles in the pollen match the alleles in the pistil tissue, a rejection cascade is triggered.
Structurally, this rejection can occur at two distinct checkpoints.
In sporophytic self-incompatibility (SSI), the rejection typically occurs right at the stigma surface, immediately preventing the pollen from hydrating or germinating.
In gametophytic self-incompatibility (GSI), the pollen is allowed to germinate, but the rejection occurs as it travels through the style.
Statement 3 is incorrect because, during a stylar SI reaction, the growth of the pollen tube is actively arrested and destroyed mid-way down the style via localized RNase enzymes.
It never reaches the ovule or the micropyle.
Self-incompatibility (SI) is the ultimate genetic barrier against inbreeding.
It operates via an S-locus with multiple alleles; if the alleles in the pollen match the alleles in the pistil tissue, a rejection cascade is triggered.
Structurally, this rejection can occur at two distinct checkpoints.
In sporophytic self-incompatibility (SSI), the rejection typically occurs right at the stigma surface, immediately preventing the pollen from hydrating or germinating.
In gametophytic self-incompatibility (GSI), the pollen is allowed to germinate, but the rejection occurs as it travels through the style.
Statement 3 is incorrect because, during a stylar SI reaction, the growth of the pollen tube is actively arrested and destroyed mid-way down the style via localized RNase enzymes.
It never reaches the ovule or the micropyle.