Outbreeding Devices and Pollen Pistil Interaction: Types & Importance

You have landed on the right page to learn about Outbreeding Devices and Pollen Pistil Interaction. Are all flowers of the same species genetically the same? If there is any genetic variation, then how does it happen? Does pollination play any role in this? Pollination is the process in which pollen grains transfer from the anther to the stigma of the same (Self-pollination) or different flower (Cross-pollination). Inbreeding or self-pollination does not bring new variations.

Outbreeding devices encourage cross-pollination through which new variations are formed. Pollen pistil interaction is the group of events that occur from the deposition of pollen over the stigma to the time of pollen tube entry into the ovule. It is required in the fertilisation of angiosperms. Continue reading to know more.

Pollination and its Types

Pollination is the transfer of pollen grains from the anther to the stigma of either the same or different flower but of the same species. It can be of two types:

a) Self-pollination: Self-pollination is the transfer of pollen grains from the anther to the stigma of the same flower.

b) Cross-pollination: Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of a genetically different flower.

 Fig: Types of Pollination

What are Outbreeding Devices?

Outbreeding devices are devices or features of plants that discourage self-pollination and encourage cross-pollination. It brings genetic variation and prevents inbreeding depression, which may be a result of continued self-pollination.

Common Outbreeding Devices

Some common outbreeding devices are:

1. Dicliny (Unisexuality): Formation of unisexual flowers with either of the two conditions:

(i) Monoecious plants produce male and female flowers on the same plant. This prevents autogamy but not geitonogamy. e.g., Castor, maize.
(ii) Dioecious plants produce male and female flowers on two separate plants. It prevents autogamy as well as geitonogamy. e.g., Vallisneria, papaya.

Fig: Unisexuality

2. Dichogamy: When the stigma and stamens of a bisexual flower mature at different times are known as dichogamy.

(i) Protandry: The pollen is released before the stigma becomes receptive. (Example:  Sunflower, Cotton, Clerodendrum, etc.). 
(ii) Protogyny: The stigma becomes receptive much before the release of pollen (Example: Ficus, Aristolochia, Scrophularia, etc.).

Fig: Dichogamy

3. Pollen prepotency: Pollen grains of different flowers germinate more rapidly over the stigma than the pollen grains of the same flower, thus preventing autogamy. Example: Apple, Grape.

4. Self-incompatibility: Self-incompatibility is a genetically controlled mechanism where pollen is not able to fertilise the same flower or other flowers on the same plant. This is caused due to inhibition of the growth of the pollen tube in the stigma and style, thereby averting the entry of male gametes to the ovules.

  Fig: Self-incompatibility

5. Herkogamy: When self-pollination becomes impossible due to some barrier between male and female reproductive parts, self-pollination is discouraged. Example: Iris, Clerodendron, etc.

   Fig: Herkogamy

6. Heterostyly: In some plants like Calotropis, Salvia, etc., the anther and stigma are placed at different positions so that the pollen grain cannot come in contact with the stigma and pollinate it.

  Fig: Heterostyly

Significances of Outbreeding Mechanism

1. Inbreeding Depression: If self-pollination is continued year after year, then there are chances of inbreeding depression which results in infertility. Outbreeding devices help to overcome inbreeding depression
2. No genetic variations: Due to the presence of the same genes, there are no new variations taking place. Genetic variations are required for new varieties. Outbreeding helps to bring new genetic combinations and thus variations.

Pollen Pistil Interaction

i. The group of events that occur from the deposition of pollen over the stigma to the time of pollen tube entry into the ovule is together referred to as pollen – pistil interaction.
ii. It is a dynamic process that helps to identify the pollen belonging to the same species or from different species.
iii. The pistil has the power to recognise the pollen, whether it is the right type (compatible) or the wrong type (incompatible).
iv. The recognition of compatibility or incompatibility of pollen-pistil interaction is followed by a special type of chemicals like boron, inositol, and sucrose levels.
v. After recognition of the correct pollen, the post–pollination events take place, which leads to fertilisation.
vi. The compatible pollen grains reach the receptive stigma of the carpel by the act of pollination.
vii. The compatible pollens can absorb water and nutrients from the surface of the stigma.
viii. They germinate and produce pollen tubes.
ix. The pollen tube grows into the style and reaches the ovary.
x. The growth of the pollen tube is chemotropic.
xi. The generative cell divides and forms two male gametes during the growth of the pollen tube in the stigma if pollen grains are shed at two-celled conditions.
xii. If pollen grains are shed at three-celled stages, the pollen tube carries two male gametes from the beginning.
xiii. The entry of the pollen tube to the embryo sac may take one of these routes:
In porogamy, it enters through the micropyle. Example: Lily, etc.
In chalazogamy, it enters through chalaza. Example: Casuarina, etc.
In mesogamy, it enters by piercing the integuments. Example: Cucurbita, etc.

Learn the Concepts of Pollination

Fig: Entry of Pollen tube into the ovule

xiv. Irrespective of the place of entry of the pollen tube into the ovule, the tube invariably enters the embryo sac at the micropylar end by degenerating synergid cells.
xv. The filiform apparatus present at the micropylar part of synergids guides the entry of the pollen tube.

 Fig: Pollen-pistil interaction

Importance of Pollen-pistil Interaction

The knowledge of pollen-pistil interaction helps the plant breeders in manipulating pollen growth even in incompatible cases to get desired hybrids.

Summary

Outbreeding devices are devices or features of plants that discourage self-pollination and encourage cross-pollination. It prevents the loss of genetic variation or inbreeding depression, which may be a result of continued self-pollination. Some outbreeding devices are dicliny, dichogamy, pollen prepotency, self-incompatibility, herkogamy, and heterostyly.

The group of events that occur from the deposition of pollen over the stigma to the time of pollen tube entry into the ovule is together referred to as pollen – pistil interaction. It is a dynamic process that has checks at several places for the promotion or inhibition of pollen tubes. 

Learn About Reproduction In Flowering Plants

Frequently Asked Questions

Q.1. What are outbreeding devices?
Ans: The devices or features of plants that discourage self-pollination and encourage cross-pollination are called outbreeding devices.

Q.2. Name the outbreeding devices used by plants to prevent self-pollination.
Ans: The outbreeding devices used by plants to prevent self-pollination are dicliny, dichogamy, pollen prepotency, self-incompatibility, herkogamy, and heterostyly.

Q.3: What is pollen-pistil interaction?
Ans: The group of events that occur from the deposition of pollen over the stigma to the time of pollen tube entry into the ovule is together referred to as pollen – pistil interaction.

Q.4. What is porogamy?
Ans: When the pollen tube enters the ovule through the micropyle, then it is called porogamy.

Q.5. What do you mean by pollen prepotency?
Ans: Pollen grains of different flowers germinate more rapidly over the stigma than the pollen grains of the same flower, thus preventing autogamy.

We hope this detailed article on outbreeding devices and pollen pistil interaction helped you in your studies. If you have any doubts, queries or suggestions regarding this article, feel to ask us in the comment section and we will be more than happy to assist you. Happy learning!