Pollination

Pollination is the biological process by which pollen from the male part of the flower transfers to the female part of the same or on different flowers. Pollination results in fertilization and the production of seeds. Pollination is important for the reproduction of plants. Pollination can occur in different ways, such as through the wind, water, or animals such as bees, butterflies, and many more. However, some plant species are self-pollinating or do not require pollinators to reproduce.

What is Pollination?

Pollination can be defined as the transfer of pollen from an anther the male part of the plant to the stigma, which is the female part of the plant. Pollen can be transmitted through animals such as insects and birds, and also through water, wind, etc., and they are known as pollinating agents. Stamen will interact with the stigma of the same species of flower, so it is important that stamen will reach the stigma of the same family plant for successful pollination. 

Process of Pollination

Pollination begins with the transfer of pollen grains to the stigma in a flower of a plant, when pollen grain reaches then a pollen tube will be formed with the style length that basically connects the stigma and ovary. When the pollen tube is completely formed the pollen grain will start transmitting sperms to the ovary.

When the sperm cell (Pollen grains) reaches the ovary the fertilization process will begin and the seed will be released from the parent and allowed to grow into a plant and then continue its reproductive cycle using the pollination method.

Also Read: Androecium

Agents of Pollination

During sexual reproduction, these agents of pollination are the ones who transfer pollen grains from one to flower or plant.  It is classified based on Anatomy and on what types of forces are involved. 

Classification based on Anatomy

1. Syndromic agents: These agents can be insects or animals that feed on nectar. Basically while gathering food, these agents attach pollens with themselves and make themselves pollinating agents in cross-pollination.
2. Proboscis agents: These agents are animals that feed through their long tongues called proboscis. They basically collect pollen from one plant while feeding and then transfer it to another plant.

Classification based on what types of forces are involved

1. Abiotic factors- agents that use physical forces. For example- wind, water, rain, etc.
2. Biotic factors -  agents that work with living organisms. For example- insects such as bees, butterflies, etc.

Types of Pollination

Plants having flowers depend on pollination for reproduction. There are two types of pollination:

• Self Pollination
• Cross-Pollination

Self Pollination

Self-pollination occurs when pollen grains are transferred from the anther of one flower of a plant to the stigma in the same flower of the same plant. It can also occur when pollen grains are transferred from the anther of one flower of one plant to the stigma of another flower but of the same plant. During self-pollination, the eggs and sperm of the same flower share the same genetic information which leads to a reduction in genetic diversity.

Advantages of Self-Pollination

1. Less wastage of pollen grains as compared to cross-pollination.
2. It ensures a standard harvest quality in vegetable gardening and farming.
3. It ensures the elimination of recessive characters.
4. It doesn't rely on any pollinators like bees, water, wind, etc.
5. They require less effort than plants as they don't need pollinators.
6. It ensures that even a small quantity of produced pollens from plants can achieve a good success rate in the population.

Disadvantages of  Self-Pollination

The primary disadvantage of self-pollination is that gene mixing not occurred in self-pollination.

1. Seeds will be less in number.
2. Due to reduced genetic diversity, the offspring will have less immunity to diseases.

Cross-Pollination

Cross-pollination occurs when pollen grains are transferred from the anther of one flower of one plant to the stigma of another flower of another plant. During cross-pollination, the eggs and sperms will share their different genetic information which leads to an increase in genetic diversity. While combining the different genetic information the offspring will become unique. 

Types of Cross-pollination

Cross-Pollination occurred via both biotic and abiotic factors. Following are the 

Pollination by Animals-Zoophily

Basically, this is the pollination that is done by animals. Animals play an essential role in plant reproduction as they help in seed dispersal. The animals spread the seeds as they eat fruits from one plant and move to another new location.

Pollination by Wind-Anemophily

Basically, this is the pollination that is done by the wind. When pollens are transferred to the female part of the plant that is stigma through the wind.

Artificial Pollination-Anthropophily

Basically, this is artificial pollination which means pollination is done by human beings. This is done by spreading the pollen grains over the female part of the plant. The hybridization technique can be used in this process.

Advantages of Cross-Pollination 

The following are the advantages of cross-pollination:

1. New varieties of crops and plants can be formed.
2. All unisexual plants can involve in cross-pollination.
3. Offspring will be healthier as there is an increase in genetic diversity during cross-pollination.
4. Produced seeds will be more viable.

Disadvantages of  Cross-Pollination

1. More wastage of pollen grains as compared to self-pollination.
2. During meiosis, genetic recombination will create chances of eliminating the good characters and adding unnecessary characters in offspring. 

Mechanism that Prevents Self-pollination

Two noticeable mechanisms that prevent self-pollination are:

1. Natural Way
2. Chemical Way

The natural way is dichogamy. A situation in which pollen grains are shed either before or after the period during which the stigma of the same plant is receptive.

The chemical way is Chemical self-incompatibility. Basically, this depends upon the chemical substances that are already present in the plant, pollen may not grow on the stigma of the same flower that produced it. Alternatively, the pollen tube may not be able to fertilize by growing the stem normally after germination. Chemical incompatibility is usually not found in plants that have strong temporal or structural barriers to self-pollination. The formation of such a mechanism during evolution was clearly sufficient for most plant species.

Mechanism that Permits Self-pollination

• Perfect flower: This type of flower also called bisexual and hermaphroditic flower, is self-fertilized by being present in a single plant because both male and female reproductive organs are present in the same flower. It will be promoted. When pollen release and stigma receptivity are synchronized and there is no mechanism to facilitate pollen transfer from flower to flower, pollen transfer within the flower is guaranteed.
• Homogamy: Female and male reproductive organs mature at the same time. That is, pollen is released as soon as the stigma is absorbed.
• Cleistogamy: This is a plant mechanism in which pollination and fertilization occur before or just before flowering.