Pollination
$\displaystyle \small \bullet$ Transfer of pollen grains from anther to stigma is called pollination.
$\displaystyle \small \bullet$ Types of pollination depending on source of pollen
1. Autogamy:
$\displaystyle \small \circ$ Self pollination
$\displaystyle \small \circ$ The flower is pollinated by its own pollen.
$\displaystyle \small \circ$ It is possible only when the flower is bisexual, i.e. contains both stamens and carpels.
$\displaystyle \small \circ$ Chasmogamous flowers: opens and exposes anthers and stigma.
$\displaystyle \small \circ$ Cleistogamous flowers: do not open. When anthers dehisce in the flower buds, pollen grains come in contact with the stigma to effect pollination. Flowers produce assured seed-set even in the absence of pollinators. Ex: Viola (common pansy), Oxalis, and Commelina.
2. Geitonogamy:
$\displaystyle \small \circ$ It is functionally cross-pollination involving a pollinating agent but genetically self pollination.
$\displaystyle \small \circ$ The pollen from one flower are deposited on the stigma of another flower of same plant.
$\displaystyle \small \circ$ Flowers could be bisexual or unisexual but are borne by the same parent plant.
$\displaystyle \small \circ$ It may need an external agency like wind or insects.
3. Xenogamy:
$\displaystyle \small \circ$ Cross pollination
$\displaystyle \small \circ$ It is the transfer of pollens from the anther of one plant to the stigma of another plant of same species.
$\displaystyle \small \circ$ It involves two separate plants and outside agencies like wind, water or insects.
Advantages of self- pollination
$\displaystyle \small \circ$ In self- pollination, there is no diversity in the genes and therefore the purity of the race is maintained.
$\displaystyle \small \circ$ The plants do not depend on external factors for pollination and even smaller quantities of pollen grains have a good success rate in getting pollinated.
$\displaystyle \small \circ$ Self- pollination ensures that recessive characters are eliminated.
Disadvantages of self- pollination
$\displaystyle \small \circ$ Since there is no mixing up of genes, there are no new characters or features that are introduced into the lineage of the offsprings.
$\displaystyle \small \circ$ Self- pollination is said to reduce the vigor and vitality of the race as there are no new features introduced.
$\displaystyle \small \circ$ Without new characters introduced, the resultant offspring's immunity to diseases reduces.
Advantages of cross-pollination
$\displaystyle \small \circ$ Cross-pollination is beneficial to the race of the plant as it introduces new genes into the lineage as a result of the fertilization between genetically different gametes
$\displaystyle \small \circ$ Cross-pollination improves the resistance of the offsprings to diseases and changes in the environment.
$\displaystyle \small \circ$ The seeds produced as a result of cross-pollination are good in vigor and vitality.
$\displaystyle \small \circ$ If there are any recessive characters in the lineage, they are eliminated as a result of genetic recombination.
$\displaystyle \small \circ$ It is the only way unisexual plants can reproduce.
Disadvantages of cross-pollination
$\displaystyle \small \circ$ There is a high wastage of pollen grains that need to be produced to ensure fertilization occurs.
$\displaystyle \small \circ$ There are high chances that the good qualities may get eliminated and unwanted characteristics may get added due to recombination of the genes.
Agents of Pollination
Agents of pollination could be abiotic (water, wind) and biotic (insects, butterfly, honey bee etc.)
Large number of pollen grains are produced by plants using abiotic mode of pollination as most of pollen grains are wasted during transfer.
Adaptations/Modifications in flowers for Pollination
Wind Pollination (Anemophily): Pollens are carried away by wind. Plants do not produce nectar.
Pollen grains: light, non- sticky, winged, huge quantity
Anther: well exposed
Stigma: large and feathery
Flower: small, usually green, one ovule, arranged as inflorescence
Ex: corn cob, cotton, date palm, coconut palm, Cannabis (bhang), maize, walnuts, oats etc.
Water Pollination (Hydrophily): Occurs rarely and occurs in plants totally submerged in water. Plants do not produce nectar.
Bryophytes, Pteridophytes, Algae
Pollen grains: protected by mucilaginous covering
Ex: Fresh water plants - Vallisneria, Hydrilla, Sea grass- Zostera
Insect Pollination (Entomophily): Flowers get pollinated by insects and in return the insects get food in the form of nectar or pollens. Also provides safe place for laying eggs.
Pollen grains: large, sticky, less pollen
Stigma: sticky
Flowers: large, colorful, fragrant, rich in nectar
Ex: bees, butterflies, flies, beetles, wasps, ants, moths etc.
Outbreeding Devices
$\displaystyle \small \bullet$ Continued inbreeding or self- fertilization leads to a condition called as inbreeding depression.
$\displaystyle \small \bullet$ This condition is characterized by homozygous genes which are not as vital as they need to be leading to unhealthy offsprings.
$\displaystyle \small \bullet$ In self- pollination, since both the male and female gametes share the same genes, there is no genetic variation seen which is necessary for a better, more productive offspring.
$\displaystyle \small \bullet$ So, most plants have many mechanisms that they employ to avoid self -pollination and promote cross-pollination.
$\displaystyle \small \bullet$ Outbreeding devices are
1. Unisexuality: It refers to the separation of sexes. The male and the female flowers are present on the same or different plants.
Ex: papaya, palm
2. Dichogamy: in some bisexual flowers, the anthers and stigma mature at different times
$\displaystyle \small \circ$ Protandry: In this type, the androecium matures earlier than the gynoecium. Ex: maize plant, sunflower, marigold
$\displaystyle \small \circ$ Protogyny: In this type, the gynoecium matures earlier than the androecium. Ex: banyan
3. Self-incompatability (self-sterility): The gametes originating even from genetically similar plant species fail to fuse with each other. Ex: grasses, orchids
4. Anther and stigma are placed at different position so that the pollen cannot come in contact with the stigma of the same flower.
Pollen-Pistil interaction
$\displaystyle \small \bullet$ Pollination does not guarantee the transfer of the right type of pollen.
$\displaystyle \small \bullet$ The pistil has the ability to recognize the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible).
$\displaystyle \small \bullet$ Pistil accepts the right type and promotes post-pollination events that leads to fertilization.
$\displaystyle \small \bullet$ Pistil rejects the wrong type by preventing pollen germination on the stigma or pollen tube growth in the style.
$\displaystyle \small \bullet$ The pistil is the female reproductive part of a flowering plant comprising of the ovary, style, and stigma.
$\displaystyle \small \bullet$ The pollen-pistil interaction begins with pollination, followed by pollen adhesion to the stigma.
$\displaystyle \small \bullet$ After it adheres, it imbibes water and gets hydrated which initiates pollen tube germination.
$\displaystyle \small \bullet$ This pollen tube penetrates through the stigma and the tube grows through the style and reaches the ovary.
$\displaystyle \small \bullet$ Once it reaches the ovary, the tube penetrates it and reaches the micropyle of the ovule and enters into the embryo sac.
$\displaystyle \small \bullet$ Here, the two male nuclei fuse with the megaspore and the vegetative nucleus to form the diploid zygote and the triploid endosperm respectively.
$\displaystyle \small \bullet$ This fusion of the male and female gametes is known as fertilization.
Artificial Hybridization
$\displaystyle \small \bullet$ Knowledge on Pollen-pistil interaction helps in crossing different species/genera to produce commercially superior varieties.
$\displaystyle \small \bullet$ Artificial hybridization is the process in which only desired pollen grains are used for pollination & fertilization.
$\displaystyle \small \bullet$ Artificial hybridization is achieved using the following techniques
Emasculation
$\displaystyle \small \circ$ Removal of anthers from bisexual flowers of female parent plant.
$\displaystyle \small \circ$ This is done before anthers mature.
$\displaystyle \small \circ$ Prevents self-pollination.
Bagging
$\displaystyle \small \circ$ Covering the emasculated flower to prevent contamination.
$\displaystyle \small \circ$ Prevents contamination with unwanted pollen.
$\displaystyle \small \circ$ Desired pollen grains are dusted on stigma.
$\displaystyle \small \circ$ Flowers are bagged again.
$\displaystyle \small \bullet$ Transfer of pollen grains from anther to stigma is called pollination.
$\displaystyle \small \bullet$ Types of pollination depending on source of pollen
1. Autogamy:
$\displaystyle \small \circ$ Self pollination
$\displaystyle \small \circ$ The flower is pollinated by its own pollen.
$\displaystyle \small \circ$ It is possible only when the flower is bisexual, i.e. contains both stamens and carpels.
$\displaystyle \small \circ$ Chasmogamous flowers: opens and exposes anthers and stigma.
$\displaystyle \small \circ$ Cleistogamous flowers: do not open. When anthers dehisce in the flower buds, pollen grains come in contact with the stigma to effect pollination. Flowers produce assured seed-set even in the absence of pollinators. Ex: Viola (common pansy), Oxalis, and Commelina.
2. Geitonogamy:
$\displaystyle \small \circ$ It is functionally cross-pollination involving a pollinating agent but genetically self pollination.
$\displaystyle \small \circ$ The pollen from one flower are deposited on the stigma of another flower of same plant.
$\displaystyle \small \circ$ Flowers could be bisexual or unisexual but are borne by the same parent plant.
$\displaystyle \small \circ$ It may need an external agency like wind or insects.
3. Xenogamy:
$\displaystyle \small \circ$ Cross pollination
$\displaystyle \small \circ$ It is the transfer of pollens from the anther of one plant to the stigma of another plant of same species.
$\displaystyle \small \circ$ It involves two separate plants and outside agencies like wind, water or insects.
Advantages of self- pollination
$\displaystyle \small \circ$ In self- pollination, there is no diversity in the genes and therefore the purity of the race is maintained.
$\displaystyle \small \circ$ The plants do not depend on external factors for pollination and even smaller quantities of pollen grains have a good success rate in getting pollinated.
$\displaystyle \small \circ$ Self- pollination ensures that recessive characters are eliminated.
Disadvantages of self- pollination
$\displaystyle \small \circ$ Since there is no mixing up of genes, there are no new characters or features that are introduced into the lineage of the offsprings.
$\displaystyle \small \circ$ Self- pollination is said to reduce the vigor and vitality of the race as there are no new features introduced.
$\displaystyle \small \circ$ Without new characters introduced, the resultant offspring's immunity to diseases reduces.
Advantages of cross-pollination
$\displaystyle \small \circ$ Cross-pollination is beneficial to the race of the plant as it introduces new genes into the lineage as a result of the fertilization between genetically different gametes
$\displaystyle \small \circ$ Cross-pollination improves the resistance of the offsprings to diseases and changes in the environment.
$\displaystyle \small \circ$ The seeds produced as a result of cross-pollination are good in vigor and vitality.
$\displaystyle \small \circ$ If there are any recessive characters in the lineage, they are eliminated as a result of genetic recombination.
$\displaystyle \small \circ$ It is the only way unisexual plants can reproduce.
Disadvantages of cross-pollination
$\displaystyle \small \circ$ There is a high wastage of pollen grains that need to be produced to ensure fertilization occurs.
$\displaystyle \small \circ$ There are high chances that the good qualities may get eliminated and unwanted characteristics may get added due to recombination of the genes.
Agents of Pollination
Agents of pollination could be abiotic (water, wind) and biotic (insects, butterfly, honey bee etc.)
Large number of pollen grains are produced by plants using abiotic mode of pollination as most of pollen grains are wasted during transfer.
Adaptations/Modifications in flowers for Pollination
Wind Pollination (Anemophily): Pollens are carried away by wind. Plants do not produce nectar.
Pollen grains: light, non- sticky, winged, huge quantity
Anther: well exposed
Stigma: large and feathery
Flower: small, usually green, one ovule, arranged as inflorescence
Ex: corn cob, cotton, date palm, coconut palm, Cannabis (bhang), maize, walnuts, oats etc.
Water Pollination (Hydrophily): Occurs rarely and occurs in plants totally submerged in water. Plants do not produce nectar.
Bryophytes, Pteridophytes, Algae
Pollen grains: protected by mucilaginous covering
Ex: Fresh water plants - Vallisneria, Hydrilla, Sea grass- Zostera
Insect Pollination (Entomophily): Flowers get pollinated by insects and in return the insects get food in the form of nectar or pollens. Also provides safe place for laying eggs.
Pollen grains: large, sticky, less pollen
Stigma: sticky
Flowers: large, colorful, fragrant, rich in nectar
Ex: bees, butterflies, flies, beetles, wasps, ants, moths etc.
Outbreeding Devices
$\displaystyle \small \bullet$ Continued inbreeding or self- fertilization leads to a condition called as inbreeding depression.
$\displaystyle \small \bullet$ This condition is characterized by homozygous genes which are not as vital as they need to be leading to unhealthy offsprings.
$\displaystyle \small \bullet$ In self- pollination, since both the male and female gametes share the same genes, there is no genetic variation seen which is necessary for a better, more productive offspring.
$\displaystyle \small \bullet$ So, most plants have many mechanisms that they employ to avoid self -pollination and promote cross-pollination.
$\displaystyle \small \bullet$ Outbreeding devices are
1. Unisexuality: It refers to the separation of sexes. The male and the female flowers are present on the same or different plants.
Ex: papaya, palm
2. Dichogamy: in some bisexual flowers, the anthers and stigma mature at different times
$\displaystyle \small \circ$ Protandry: In this type, the androecium matures earlier than the gynoecium. Ex: maize plant, sunflower, marigold
$\displaystyle \small \circ$ Protogyny: In this type, the gynoecium matures earlier than the androecium. Ex: banyan
3. Self-incompatability (self-sterility): The gametes originating even from genetically similar plant species fail to fuse with each other. Ex: grasses, orchids
4. Anther and stigma are placed at different position so that the pollen cannot come in contact with the stigma of the same flower.
Pollen-Pistil interaction
$\displaystyle \small \bullet$ Pollination does not guarantee the transfer of the right type of pollen.
$\displaystyle \small \bullet$ The pistil has the ability to recognize the pollen, whether it is of the right type (compatible) or of the wrong type (incompatible).
$\displaystyle \small \bullet$ Pistil accepts the right type and promotes post-pollination events that leads to fertilization.
$\displaystyle \small \bullet$ Pistil rejects the wrong type by preventing pollen germination on the stigma or pollen tube growth in the style.
$\displaystyle \small \bullet$ The pistil is the female reproductive part of a flowering plant comprising of the ovary, style, and stigma.
$\displaystyle \small \bullet$ The pollen-pistil interaction begins with pollination, followed by pollen adhesion to the stigma.
$\displaystyle \small \bullet$ After it adheres, it imbibes water and gets hydrated which initiates pollen tube germination.
$\displaystyle \small \bullet$ This pollen tube penetrates through the stigma and the tube grows through the style and reaches the ovary.
$\displaystyle \small \bullet$ Once it reaches the ovary, the tube penetrates it and reaches the micropyle of the ovule and enters into the embryo sac.
$\displaystyle \small \bullet$ Here, the two male nuclei fuse with the megaspore and the vegetative nucleus to form the diploid zygote and the triploid endosperm respectively.
$\displaystyle \small \bullet$ This fusion of the male and female gametes is known as fertilization.
Artificial Hybridization
$\displaystyle \small \bullet$ Knowledge on Pollen-pistil interaction helps in crossing different species/genera to produce commercially superior varieties.
$\displaystyle \small \bullet$ Artificial hybridization is the process in which only desired pollen grains are used for pollination & fertilization.
$\displaystyle \small \bullet$ Artificial hybridization is achieved using the following techniques
Emasculation
$\displaystyle \small \circ$ Removal of anthers from bisexual flowers of female parent plant.
$\displaystyle \small \circ$ This is done before anthers mature.
$\displaystyle \small \circ$ Prevents self-pollination.
Bagging
$\displaystyle \small \circ$ Covering the emasculated flower to prevent contamination.
$\displaystyle \small \circ$ Prevents contamination with unwanted pollen.
$\displaystyle \small \circ$ Desired pollen grains are dusted on stigma.
$\displaystyle \small \circ$ Flowers are bagged again.
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