What is Pollen Pistil Interaction?
Pollen pistil interaction is the process of transfer of pollen grains of one plant to the pistil/stigma of the same or different plant, which can be either self or cross-pollination. The pistil is the female reproductive part of a flowering plant, while pollen grains are the male reproductive part of a plant. Pollination is the first step of pollen pistil interaction, followed by the pollen adhesion to the stigma. Now, we'll be heading towards our next section, which is a pretty interesting one: the concept of outbreeding devices in plants.
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Relation Between Pollen Pistil Interaction and Outbreeding Devices
The section is related to the concept of outbreeding devices and the relationship between pollen pistil interaction and outbreeding devices. Before proceeding to the types of outbreeding devices, let’s understand what outbreeding devices are.
What is The Meaning of Outbreeding Devices?
Outbreeding devices are the mechanisms/processes which the plants adapt to prevent self-pollination. But why do plants use such devices? The important reasons are mentioned below.
Inbreeding Depression: The reason behind the adoption of such techniques by plants is that due to continued inbreeding, plants can develop a condition called inbreeding depression, leading to unhealthy offspring.
No Genetic Variations: in self-pollination, due to the same genes of males and females, there are no genetic variations.
Unisexuality: If the plant is unisexual, Outbreeding is the only alternative.
Unsynchronized Pollen Release: The release of pollen grains and receptivity of stigma should be synchronized for the breeding to happen. This prevents self-pollination.
Now, let’s get into the prime topic of the section- the types of outbreeding devices.
Outbreeding Devices
There are several devices that the plants adapt to promote cross-pollination, which are enumerated below:
Unisexuality: Unisexuality is an outbreeding device in which the plant bears, either male or female flowers. Besides, the flower is also not hermaphrodite. This is also known as Dioecism.
Dichogamy: In this outbreeding device, the stigma and the anther have different maturity times. Thus, depending upon the maturity, Dichogamy can be classified into two types:
Protandry: The androecium matures before the gynoecium. For example, maize plants.
Protogyny: The gynoecium matures before the androecium.
Herkogamy: Herkogamy is a naturally occurring condition where there is a natural physical barrier to the entry of pollen grains into the ovaries.
Self-Sterility: In this outbreeding device, the plant possesses a gene to recognize similar genes and doesn’t allow the pollen grain to germinate. The self-sterile gene is present in the ovule and the grain.
Heterostyly: In this outbreeding device, the stigma and the anther differ in levels, preventing the pollen grain to reach the stigma and pollinating it.
Pollen Prepotency: In pollen prepotency, a different flower's pollen matures faster than that of the same flower, thus helping in preventing autogamy.
These are the outbreeding devices in plants. Now, if the question comes- Explain pollen pistil interaction and Outbreeding devices, one will be able to answer easily. The next section is the final section of the discussion and enumerates the steps of pollen pistil interaction.
Steps of Pollen Pistil Interaction
Pollination doesn’t always mean fertilization. For pollination to occur, the pistil needs to recognize the pollen grain of the same species. Pollen pistil interaction is not a small process. Thus, we need to understand the complete process of pollen pistil interaction, which results in successful fertilization. Enumerated below are the steps of pollen pistil interaction:
The male plant releases pollen grains.
The pollen grain lands on the pistil of the female plant.
If the pollen is compatible, the pistil accepts it, while incompatible ones are rejected.
If the pollen grain is accepted by the female plant, the grain forms pollen tubes and releases its contents and chemicals.
The pollen tubes head towards the ovary through style.
As the pollen tube reaches the ovary, the male gamete enters the ovary and is then synergic.
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This is the complete process of the pollen pistil interaction process that is required for successful fertilization.
We hope that all the concepts related to pollen pistil interactions and outbreeding devices in plants are pretty much clear. We have learned about both the steps of pollen pistil interaction as well as the different outbreeding devices.
FAQs on Pollen Pistil Interaction
1. What is pollen-pistil interaction in flowering plants?
Pollen-pistil interaction is the dynamic sequence of events that unfolds from the moment a pollen grain lands on the stigma until the pollen tube successfully enters the ovule. This process is a critical checkpoint in plant reproduction, involving a dialogue between the pollen and the pistil. It ensures that only compatible pollen of the same species is allowed to germinate and fertilize the egg, while rejecting incompatible or foreign pollen.
2. What are the key events that occur after a compatible pollen grain lands on the stigma?
Once a compatible pollen grain is accepted by the stigma, a series of crucial events takes place:
- Pollen Germination: The pollen grain absorbs moisture and nutrients from the stigma and germinates, forming a pollen tube.
- Pollen Tube Growth: The pollen tube grows down through the style, navigating towards the ovary, guided by chemical signals from the synergid cells.
- Entry into Ovule: The pollen tube enters the ovule, typically through the micropylar end, and reaches the embryo sac.
- Discharge of Male Gametes: The pollen tube releases its two male gametes into the cytoplasm of one of the synergids, preparing for double fertilisation.
3. What are outbreeding devices and why are they important for plants?
Outbreeding devices are mechanisms or strategies that flowering plants have evolved to discourage self-pollination and promote cross-pollination. They are crucial because continuous self-pollination can lead to inbreeding depression, a condition where genetic uniformity reduces the fitness, vigour, and fertility of offspring over generations. By promoting cross-pollination, these devices introduce genetic variation, which is essential for adaptation and evolution.
4. Explain three major types of outbreeding devices with examples.
Three major outbreeding devices found in plants are:
- Unisexuality (Dioecy): The plant bears either only male or only female flowers. Since an individual plant cannot self-pollinate, cross-pollination is the only option. Example: Papaya.
- Dichogamy: The anthers and stigma mature at different times, preventing self-pollination. This can be protandry (anthers mature first, e.g., sunflower) or protogyny (stigma matures first, e.g., Magnolia).
- Self-incompatibility: This is a genetic mechanism where the pistil rejects pollen from the same plant or genetically similar plants. It prevents pollen germination or pollen tube growth in the style, effectively blocking self-fertilisation. Example: Tobacco, Petunia.
5. How does a pistil differentiate between compatible and incompatible pollen?
The differentiation between compatible and incompatible pollen is a highly specific process mediated by a continuous chemical dialogue. This recognition is based on the interaction between proteins and other chemical components present on the surface of the pollen grain and the stigma. If the pollen is compatible (of the right type), these interactions trigger its acceptance, hydration, and germination. If it is incompatible, the recognition system actively inhibits germination or stops the growth of the pollen tube within the style.
6. What is the fundamental difference between self-incompatibility and herkogamy as outbreeding devices?
The fundamental difference lies in their mechanism. Self-incompatibility is a genetic and physiological barrier where the pistil biochemically rejects its own pollen, preventing fertilisation even if pollination occurs. In contrast, herkogamy is a structural or physical barrier. It involves the spatial separation of the anther and stigma within a flower, such as having a long style and short stamens, making it physically difficult for pollen to land on the stigma of the same flower.
7. What would happen if a pistil could not reject incompatible pollen?
If a pistil lost its ability to reject incompatible pollen, it would lead to several negative consequences. Firstly, it could result in wasteful fertilisation attempts by pollen from different species, leading to the formation of non-viable seeds and wasting the plant's reproductive energy. Secondly, it could break down the reproductive barriers between species, potentially leading to the creation of weak or sterile hybrids. The ability to reject incompatible pollen is therefore a vital mechanism for ensuring reproductive efficiency and maintaining species integrity.
