Pollination is the transfer of pollen grains from one flower’s anther to the stigma of the same or different flower. There are two forms of pollination: Pollen grains are transferred from the anther of one plant to the stigma of another plant in a process known as self-pollination. Cross-pollination is the transfer of pollen grains from one plant’s anther to another plant’s stigma. Inbreeding refers to self-pollination, and outbreeding refers to cross-pollination.
Reasons For Outbreeding
Inbreeding depression develops as a result of continued inbreeding or self-fertilization. This syndrome is caused by homozygous genes that aren’t as important as they should be, resulting in ill kids.
Because both the male and female gametes share the same genes in self-pollination, no genetic variety is visible, which is required for a better, more productive offspring. As a result, most plants have a variety of systems in place to prevent self-pollination and favour cross-pollination.
Outbreeding Devices
Plants induce cross-pollination through a variety of ways and systems. We’ll look at a few of them in the following sections:
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Unisexuality: The plant in this circumstance is not hermaphrodite and has either male or female blooms. Another term for it is dioecism. In this mechanism, the stigma and anther mature at different times.
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Dichogamy is further subdivided into two categories based on who grows first: Protandry in which the androecium matures before the gynoecium is a type of protandry in which the androecium matures before the gynoecium. Consider a corn plant. In this kind, the gynoecium matures before the androecium.
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Herkogamy is a term used to describe phenomena in which pollen from the same flower is prevented from entering the ovary by a natural physical barrier.
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Self-sterility occurs when a gene recognises a comparable gene and inhibits the pollen grain from germinating. This is because the ovule and grain contain a self-sterile gene.
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Heterostyly: The stigma and anthers of some plants, such as the oxalis, are situated at different levels. Pollen is unable to reach the stigma and pollinate it as a result of this.
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Pollen prepotency: This mechanism prevents autogamy by allowing pollen from separate flowers to germinate faster than pollen from the same flower.
Interaction between pollen and pistils
Pollination, as detailed above, is only the initial stage in the pollen-pistil relationship. The ovary, style, and stigma make up the pistil, which is the female reproductive component of a flowering plant. Pollination precedes pollen attachment to the stigma in the pollen-pistil interaction. It imbibes water and becomes hydrated after adhering, which triggers pollen tube development.
This pollen tube passes through the stigma, develops through the style, and eventually reaches the ovary. When the tube reaches the ovary, it penetrates it and enters the embryo sac through the micropyle of the ovule. The two male nuclei join forces with the megaspore and vegetative nucleus to generate the diploid zygote and triploid endosperm, respectively. Fertilization is the process of combining male and female gametes.
Principal Significance Of Pollen Pistil Interaction
The following are the most important points of pollen-pistil interactions:
a. The most important requirement for sexual reproduction is male gamete screening and selection, which occurs during pollen pistil interaction. As a result, pollen-pistil interaction has immense potential for manipulating pollen screening, which is important for pollen quality and compatibility.
b. Under normal circumstances, the number of pollen grains deposited on the stigma is far greater than the number of ovules available for fertilisation. As a result, pollen grains compete fiercely with pistils during pollen-pistil interaction.
Only early-germinating pollen with a faster-growing pollen tube, i.e., more vigorous pollen, can resist the rigour of post-pollination competition and fertilisation. As a result of pollen grain competition during pollen-pistil interaction, the progeny’s vigour is raised. As a result, this relationship can be considered a major contributory component in blooming plants’ evolutionary success.
c. It pertains directly to plant breeding programmes. Through hybridization, a plant breeder seeks to bring together desirable traits seen in many taxa.
Plant breeders would undoubtedly be able to influence the screening process in the pistil more successfully if they had a better understanding of the biology of pollen-pistil interaction.
Conclusion
We conclude that the pistil is only found in angiosperms. It protects the pollen tube and acts as a channel for pollen tubes to grow to the ovary, but it also serves as a venue for pollen-pistil interactions, which regulate pollen tube growth and, thus, fertilisation.