Q.Flowering plants with hermaphrodite flowers have developed many reproductive strategies to ensure cross-pollination. Study the given outbreeding devices adopted by certain flowering plants and answer the questions that follow. [Table: Stigma vs Pollen grains of Plant A/B/C — Stigma of Plant A: ×, ✓, ✓; Stigma of Plant B: ✓, ×, ✓; Stigma of Plant C: ✓, ✓, ×] Note : All plants belong to the same species. × – No pollen tube growth/inhibition of pollen germination on stigma. ✓ – Pollen germination on stigma.
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Start your 14-day free trial to unlock the full solution →The table describes self-incompatibility, a genetic outbreeding device where a plant’s own pollen or pollen from genetically similar individuals is rejected, preventing self-fertilisation and promoting cross-pollination.
The table you’ve been given shows a neat experiment: pollen from three plants (A, B, and C) of the same species is placed on the stigmas of those same three plants. The results are clear — each plant’s own pollen fails to germinate (marked ×), while pollen from the other two plants succeeds (marked ✓). This is not a random failure; it is a deliberate, genetically controlled rejection. The plant is actively saying “no” to its own pollen.
This mechanism is called self-incompatibility (SI). It is one of the most important outbreeding devices in flowering plants, especially in hermaphrodite flowers where both male and female organs are present in the same bloom. Without such a device, self-pollination would be the easiest option — pollen from the anther simply falls onto the stigma of the same flower. But many plants have evolved to avoid this, because self-fertilisation reduces genetic diversity and can lead to inbreeding depression (weaker offspring).
Self-incompatibility is not a physical barrier like the separation of male and female flowers (dioecy) or differences in timing of maturity (dichogamy). It is a biochemical recognition system — the pollen and stigma “recognise” each other at the molecular level. If they are too similar (i.e., from the same plant or a close relative), the pollen tube growth is inhibited, often right at the stigma surface.
In the table, each plant’s own pollen is rejected (×), but pollen from any other plant of the same species is accepted (✓). This is the classic pattern of gametophytic self-incompatibility, where the pollen’s own genetic makeup (its haploid genome) determines whether it is accepted or rejected. The plant’s stigma can distinguish “self” from “non-self” pollen. …
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