Angiosperms Pollination

Introduction: In this chapter, Angiosperms Pollination, we will discuss in detail. Theophrastus described on Date palm pollination. The role of insects in pollination was described by Kolreuter. Transfer of pollen to stigma is known as Pollination.

Image: Angiosperm pollination

Pollination:

• The transfer of microspore (pollen grain) anther to megasporophyll (stigma) means pollen grain transfer to female via external agents known as pollination. 
• Pollen grains are motionless themselves, which means they require external agents for transference.
• Pollination occurs by water, air, animals, and other gravity factors.
• Types of Pollination: Self and Cross-pollination.

Self Pollination: 

• Pollen grains transfer to genetically related flowers.
• Types of Self Pollination: autogamy and geitonogamy.

A) Autogamy: Pollination occurs in intersexual or anther and stigma are closest. Types of autogamy pollination: homogamy, cleistogamy, and bud.

Image: Homogamy A- Catharanthus, B- Mirabilis jalapa, C- Potato, D, and E- Sunflower

1. Homogamy pollination: This pollination occurs in the same flower. Anthers and stigma come together during maturity, in chasmogamous flowers. Examples: Potato, Mirabilis, etc.
2. Cleistogamy pollination: Anthers and stigma are closed in cleistogamous flowers. Anther dehisces in the closed flower. External agencies are not required for this pollination. Examples: Oxalis, Balsam, etc.
3. Bud pollination: In this pollination, before the opening of buds in the flower, anther and stigma are ripen. Examples: wheat and rice.

B) Geitonogamy: When pollen grains are transferred to another flower on the same plant, e.g., Corn, etc.

Advantage of Self Pollination:

• It protects the maintenance of parental characters.
• Plants do not need to produce a huge amount of pollen grains.
• Removes recessive characters.

Disadvantages of Self Pollination:

• Vitality decreases.
• Immunity decreases.
• Variability reduce.

Cross-Pollination: Transference of pollen grains from one flower to a different flower. For this pollination, external agencies are required. External agencies can be biotic and abiotic.

1. Anemophily: (Wind pollination) With the help of wind, pollen grains transfer to a pistil e.g., Palm, Maize, grasses, etc.

Anemophilous Flowers: 

• These flowers are small in size.
•  flowers do not contain color. 
• Non-essential parts are not present.
• Stamens are more in number.
• Pollen grains are light in weight.
• Pollen grains are dusty.
• Pollen grains are nonsticky.
• Pollen grain formed in huge numbers.
• Approx. 130 million pollen grains formed by Mercurialis annua.
• Stigma is feathery.
• Anemophily is nondirectional.

Image: Anemophily

2. Hydrophily: (Water pollination) With the help of water, pollen grains transfer to a pistil.

• Flowers are small in size.
• Flowers are inconspicuous.
• Nectar is not present.
• Odour is also absent.
• Pollen grains are light in weight.
• Hypohydrophily and epihydrophily are types of hydrophylly.
• Zostera occurs below the water surface i.e., hypohydrophily.
• Vallisneria occurs on the water surface i.e., epihydrophily.

Zostera: 

• It is Seagrass.
• Zostera does not contain exine. 
• Long stigma is present.
• Pollens contains ribbon like structure.
• Pollens are filamentous.
• Contain the same gravity.

Ceratophyllum:

• It is a submerged plant.
• Pollen's structure is rounded.
• pollens do not contain exine.
• Male and female flowers are present on the same plant.
• Stigma is sticky.

Vallisneria:

• Produce a huge number of male flowers.
• It contains two fertile stamens.
• The female flower consists long stalk.

Image: Hydrophily pollination (Vallisneria)

3. Zoophily: (Animal pollination) With the help of animals, pollen grains transfer to a pistil.

• Most birds, bats, and insects play important role in this pollination.
• Bees and butterflies perform pollination activities.

4. Entomophily: (Insect pollination) With the help of insects, pollen grains transfer to a pistil.

• Insects can be wasps, bees, and butterflies for pollination.
• Bees take nectar and pollen grains from flowers.

Entomophilous Flower:

• They are colored.
• Butterflies attract red flowers.
• Corolla, sepals, and bracts contain bright colors.
• Some flower emits an odor.
• The flower contains nectar.
• Some flowers contain edible pollens.
• Pollen grains are covered by pollenkitt.
• Heavy pollen grains are present in these flowers.
• pollination occurs directional.
• Sticky stigma is present.
• Stigma is found inserted.
• Anthers are usually inserted.

Coevolution of Flower and pollinator:

• When two species interact with each other and one species forms modification and the other species forms capacity to adaptability.
• This modification formed in the two species i.e., coevolution.
• Mutation and natural selection help in coevolution.
• Insect pollinated flowers are rich in nectar.

5. Ornithophily: (Birds pollination) With the help of birds, pollen grains transfer to a pistil.

• The birds having long beaks.
• Tropicals are sunbirds and hummingbirds.
• They are less as compared to others.
• Red silk cotton, Bottlebrush, Agave, etc. are pollinated by birds.
• Ornithoflowers: Contains highly nectar, flowers are highly bright-colored, the scent is not present and the shape of corolla is a funnel.

6. Chiropterophily: (Bat pollination) With the help of bats, pollen grains transfer to a pistil. Pollens are transferred a long distance by bats.

Chiropterophilous Flowers:

• They contain dull colors.
• Nectar is present in a high amount.
• Pollens are also in high amounts.
• The Flowers' size is large.

Advantages of Cross-pollination:

• Introduce variations by cross-pollination.
• Increment of adaptability.
• Diseases resistant varieties are formed.
• New varieties are formed.
• Defective characters are removed.
• Yield is also high by cross-pollination.

Disadvantages of Cross-pollination:

• A high amount of pollen grains are waste by this pollination.
• Undesirable characters are formed.
• Good characters can be spoiled.

Self-pollination	Cross-pollination
Transfer of pollen to the stigma of a similar flower.	Transfer of pollen to the stigma of a different flower.
This pollination can occur in closed flowers.	This pollination occurs in only open flowers.
External agencies are not required.	External agencies are necessary.
They produce pure lines.	They formed variations.
Yield can fall with time.	Yield not fall below average.
New varieties not produce.	New varieties are produced.

 Conclusion: Pollination means the transfer of pollens towards the female gametophyte.

This article contains Angiosperms Pollination with images and well explanation.

 

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Angiosperms Life cycle

Angiosperms Life cycle

 Introduction: In this chapter, Angiosperms Life cycle, we will discuss in detail. Angiosperms bear seeds inside fruits. Flowering plants are highly evolved. The first flowering plant was recorded in China and Canada. Most flowering plants are found on earth.

Image: Angiosperm

Characteristic features:

• Angiosperms are found in hills and plains also.
• Microsporophylls and megasporophylls are present.
• Filament and anther are components of microsporophyll.
• Stigma, Style, and ovary are components of megasporophyll.
• The female gametophyte is an embryo sac formed by meiosis.
• Mainly insects help in pollination.
• Eight nucleate state is formed by female gametophyte.
• Egg apparatus, antipodal cells, and two polar nuclei are present in the embryo sac.
• Double fertilization: one male gamete + egg cell→ zygote and second male gamete + diploid secondary nucleus→ Primary endosperm nucleus (3n).
• Triploid primary Endosperm→ form→ the triploid endosperm.
• Endosperm gives nourishment to the embryo.
• Seeds are found in fruit and fruit provide protection in dispersal.
• Xylem and phloems are present.

Image: life-cycle-angiosperm

Structure of Flower:

• The modified shoot is a flower.
• Flowers have different colors, sizes, shapes, and smells.
• A flower developed on a mature plant.
• The flower contains sepals, petals, carpels, and stamens.
• Stamens (androecium) and Carpel (Gynoecium).
• The Accessory organs are sepals and petals.

Image: Flower

See Also: Angiosperms Pollination

Diversity Living World

Stamen: Male organ

• It is the male organ of a flower.
• Stamen contains anther and filament.
• The filament is long and stalk structure in the stamen.
• Anther shows fertility and broader in size.
• When one anther lobe is present, known as monothecous and two-lobe is present, known as dithecous.
• Groove help to the separation of two anther lobes.

Image: Stamen

Structure of Anther:

• It is a fertile portion in the stamen.
•  It is a bilobed structure.
• Every lobe consists of microsporangia.
• Bisporangiate is monothecous stamen.
• Tetrasporangiate is dithecous.
• Four microsporangia parallel to each other.
• Archesporial cells have parietal cells and sporogenous cells.
• Consists of the endothecium, middle layer, and tapetum.

Microsporangium:

• The outer wall and sporogenous tissue are the part of microsporangium.
• The epidermis, endothecium, middle layer, and tapetum are layers of the microsporangial wall.
• Large cells are present in endothecium and tapetum.
• Endothecium consists of fibrous thickenings.
• When middle layers are corrupt then they help in the protection of microspore mother cells.
• Tapetal cells consist of protoplasmic contents.
• Functions of Tapetum: provide nourishment to microspore mother cell and pollen grain, Amoeboid tapetum help in the exine formation of pollen grains, Secretory tapetum increase thickness of exine.

Microsporogenesis: (Formation of microspores or pollen grain)

• Microsporogenesis: microspore mother cell ➡ develop callose ➡ break plasmodesmal connections ➡ mother cell separate ➡ meiosis occurs ➡ produce haploid tetrad ➡ microspores (pollen grains). 

Anther Dehiscence:

• Mature anther ➡ contains two cavities 
• By loss of water ➡ endothecium contract ➡ form concave shape ➡ anther lobe ruptures ➡ Line of dehiscence observed ➡ yellow powdery mass ➡ appears in case of Mustard.

Structure of Pollen Grain:

• Diameter approx. 30-50 μm.
• The starch is found in the cytoplasm.
• Sporoderm is the covering of pollen grain.
• The inner layer is Intine containing pecto-cellulose.
• Sporopollenin found in Exine.
• Strong acid, alkali, enzymes, and high temperature cannot affect the sporopollenin.
• Ektexine and Endexine are components of Exine.
• The foot layer, baculate layer, and tectum are further components of Ektexine.
• Tectum provides in the design of pollen surface.
• Pollenkit consists of yellow, viscous layer, lipid, and carotenoids.
• In dicots, pollen grains contain three germ pores.
• In monocots, pollen grains contain a single germ furrow.
• Pollen grain has the ability to retain germination ability.
• Potato, brinjal, chilly, legumes, etc. have in the month of viability.
• Wheat has less than an hour of viability.
• Liquid nitrogen is used to preserve the pollen grains.
• Pollen causes Asthma and bronchitis-like disorders.
• Pollen contains protein, carbohydrates, and fats, hence they intake in form of tablets and syrups.

Image: Pollen grain

See also: Biological Classification

Protista Protozoan Plasmodium

Microgametotogenesis:

• Male gametophyte start ➡ in the microsporangium➡ young pollen grain embedded➡ into the cytoplasm➡ vacuoles push pollen grain➡ towards the wall➡ protoplast divide mitotically➡ form generative and vegetative cell➡ callose separates the cell➡ generative cell divides➡ into two male gametes (nonmotile).
• Pollen tube carries male gametes.
• Pollen tube secretes hormones.
• Pollen tube takes food.

Image: Microgametogenesis

Female reproductive organ: Pistil

• The female organ is a gynoecium of a flower.
• It can contain monocarpellary, bicarpellary, tricarpellary and multicarpellary.
• When carpels are separate then gynoecium is apocarpous.
• If carpels are not separate means they are fused then gynoecium is syncarpous.
• The pistil consists stigma, style, and ovary.
• Stigma help as a landing purpose for pollens.
• The pistil contains swollen parts i.e ovary.
• In wheat and rice single ovule is present in the ovary.
• Watermelon contains many ovules in the ovary.

Image: Gynoecium

Structure of Ovule:

• Ovule develops into the seed after the fertilization process.
• It is attached to the placenta.
• Funiculus is the stalk of an ovule.
• Orthotropous, anatropous, circinotropous, hemitropous, amphitropous and campylotropous are different types of ovules.
• The mass of parenchymatous cells present in the ovule is called nucellus.
• Micropyle is a narrow pore and present at end of the ovule.
• Chalaza is the place of origin.

Megasporogenesis: development of ovule

• Mound of nucellus ➡ over placenta ➡ integument develop ➡  from base ➡ primary archesporial cell ➡ develop ➡ archesporial cell divides into ➡ primary parietal and primary sporogenous cellm➡ primary sporogenous cell works as ➡ megaspore mother cell➡  then meiosis occurs ➡ form 4 haploid megaspore ➡ megasporogenesis.
•  Only chalazal megaspore performs functions. 

Megagametogenesis: Development of female gametophyte

• Cell enlarges ➡ mitotic division occurs ➡ produce 2 nucleate embryo sac ➡ both nuclei shift ➡ towards ends ➡ divide ➡ 4 nucleate and 8 nucleate ➡ one nucleus in middle ➡ polar nuclei ➡ 3 nuclei at ends ➡ 3 celled apparatus ➡ at the micropylar end ➡ 3 antipodal cells ➡ at chalazal end.

Structure of Embryo sac

•  Oval-shaped structure.
• It consists of 3 micropylar,3 chalazal, and 1 central.
• It consists of eight nuclei.
• Three mitosis and one meiosis occur.
•  Egg apparatus present at micropylar end.
• Antipodal cells are present at the chalazal end.

Image: Embryo sac

Conclusion: Angiosperms are cosmopolitan. Firstly angiosperm fossils were founded in China. They contain mostly bisexual flowers.

This article contains Angiosperms Life cycle with images and well explanation.

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