Tuesday, November 29, 2022

What Is Pollen Grain In Biology

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Developmental Biology Of Dispersed Pollen Grains

Study of pollen grain is called | 12 | REPRODUCTION IN ORGANISMS | BIOLOGY | SANTRA PUBLICATION …

Kundaranahalli R. Shivanna*,1 and Rajesh Tandon*,2

1Ashoka Trust for Research in Ecology and the Environment, Bengaluru, India and 2Department of Botany, University of Delhi, Delhi, India

ABSTRACT Professor Panchanan Maheshwari served as Professor and Head of the Department of Botany, University of Delhi, from 1950 to 1966 and built an internationally reputed School of integrated plant embryology. Studies carried out during and after Maheshwaris period from this School have enormously advanced our knowledge of the structural, developmental and functional aspects of embryological processes. This review covers studies carried out at the Delhi School on the developmental biology of dispersed pollen grains which operate from pollen dispersal from the anthers until pollen tubes discharge the male gametes in the embryo sac for fertilization. These events include pollen viability and vigour, pollen germination and pollen tube growth, structural details of the pistil relevant to pollen function, pollination and pollen-pistil interaction.

Factors Affecting Pollen Tube Growth

  • Carbohydrates: A little sugar in the hydration of the pollen grains while landing on the stigma prevents the pollen from bursting.
  • Boron: Pollen grains are deficient in boron, therefore stigma secretes enough boron so as to not hinder the growth of pollen tubes.
  • Calcium: The presence of calcium ions in the pollen grains promotes the population effect. Usually, pollen grains have a very small amount of calcium, but when a mass of pollen come together, a large amount of calcium is collected that promotes pollen tube formation.
  • Enzymes: Enzymes such as pectinase and cellulase promote elongation of the tube.
  • Physical Factors: Temperature plays the biggest role in the elongation of the pollen tubes. The optimum temperature range for pollen tube growth is 20-30 .
  • Entry Of Pollen Tube Into The Ovule

    The pollen tube finally reaches into the ovule. Based on the entry of the pollen tube into the ovary, there are three types of fertilization:

    • Porogamy: In this type, the pollen tube enters the ovary through the micropyle. E.g, Lily.
    • Chalazogamy: In this type, the pollen tube enters the ovary through the chalazal end. E.g, Casuarina
    • Mesogamy: In this type, the pollen tube enters the ovary through the funicle or the integuments. E.g, Cucurbita

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    Regulation Of The Asymmetric First Pollen Mitosis

    Following meiosis during early pollen development, the microspore nucleus first migrates to one side of the cell, with the formation of a large vacuole then an asymmetric mitotic cell division produces a large vegetative cell and a small generative cell, which is the male germline . Subsequently, the vegetative cell completely encloses the generative cell, which then divide to form two sperm cells . Following pollination, the vegetative cell produces a pollen tube, which grows through female tissues and delivers the sperm cells to the female gametophyte. Large-scale mutant screens and transcriptomics have identified mutations and genes involved in pollen development . Expression studies showed that the TCP16 gene, encoding a putative transcription factors, is expressed when microspores are released from the tetrad and before the first mitosis . Using a GUS reporter gene, TCP16 expression was detected at low levels at the tetrad stage and found to be much stronger afterwards in microspores with a single nucleus. TCP16 expression subsequently decreases gradually, becoming undetectable in the mature pollen. Its requirement for normal early microspore development is supported by RNAi analysis that showed defects at the unicellular stage , including anucleated microspores soon after release from the tetrad, with an increased frequency at the uninucleate stage.

    J.P. Mascarenhas, in, 1971

    Pollen Grains: Process Fertilization Pollination Types

    Through which route the pollen tube enters the ovule class 12 biology CBSE

    Content Editor| Updated On -Apr 13, 2022

    Pollen can be defined as a bristly or fine powder that consists of microgametophytes and mass produces sperm cells or male gametes. The branch of biology that focuses on the study of pollen and its properties is called Palynology. Pollen grains are transferred by wind, water, air, birds, insects, animals to the female plants for the objective of fertilization. In this article, we will explore the type, structure, process of transfer, and sample questions for pollen grains.

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    Where Does Pollen Form

    In the male Pollen parts, the pollen is formed in the microsporangia. In the female plant, the pollen is produced in the anthers, also called angiosperms. The microsporocyte is diploid, and it forms four haploid cells, which are called microspores. This process is called microsporogenesis. These four microspores then form the walls of the pollen grains using a material called callose. This callose is digested by callase, and only after this, the pollen grain completes the formation of endospore and exospore.

    Structure Of Pollen Grains

    Pollen grains are microscopic structures varying in their size and structure. The size of pollen grains generally varies with the species. Overall, the exact size of pollen grain ranges between three and two hundred micrometres or microns. The shape of the pollen grain is commonly found in round, ovule, triangular, disc or in a bean-shape with a smooth to spiky texture. The natural colour of pollen grains are white, which may also vary depending on the plant species. Some are yellow in colour, or orange, or cream and so on.

    Pollen grains consist of three parts:

  • The inside of the cell, which is filled with living cytoplasm, deteriorates rapidly during fossilisation.
  • Intine, the inner layer of the cell wall comprises the cellulose and pectin. Similar to the cytoplasm, the intine also degrades rapidly during fossilisation.
  • Exine, the outer layer of the cell wall, mainly consists of sporopollenin. It is one of the most resistant substances. It is an N-free polymeric substance belonging to the diverse class of organic compounds called terpenes.
  • This article concludes an introduction to pollen, pollen grains and their physical features. To know more about pollen grains, their types, functions, other related topics and important questions, keep visiting our website at

    Put your understanding of this concept to test by answering a few MCQs. Click Start Quiz to begin!

    Select the correct answer and click on the Finish buttonCheck your score and answers at the end of the quiz

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    Pollen Mutation In Single

    One of the best uses of forward mutation in single-cell omics is pollen development. In Arabidopsis, the directed isolation of mutants and their associated genes affecting pollen development has provided vital information on the spatiotemporal expression of key genes in the development of the male gametophyte. Extensive screening for abnormal pollen in mutagenized populations including those obtained from T-DNA insertion/transposon-induced mutation such as limpet pollen and the progamic phase of Arabidopsis identified LOB domain family protein SIDECAR POLLEN , the MAP215-family GEMINI POLLEN1 , TWO-IN-ONE fused kinase , and germline-specific transcription factor DUO POLLEN1 . All these mutants have provided vital information regarding molecular insights into pollen development in plants . Verelst et al. profiled the pollen of double and triple mutants of Arabidopsis, disclosing a novel insight into the complexity of the MIKC transcription factor that directs a cellular differentiation network during pollen maturation.

    J.S. Carmichael, in, 2003

    Examples Of Pollen Grain In A Sentence

    Pollen grains are formed in | 12 | SEXUAL REPRODUCTIO IN FLOWERING PLANTS | BIOLOGY | ERRORLESS…

    pollen grain The Arizona Republicpollen grain Forbespollen grains Washington Postpollen grains National Geographicpollen grains Quartzpollen grains Science | AAASpollen grainsArs Technicapollen grainsNew York Times

    These example sentences are selected automatically from various online news sources to reflect current usage of the word ‘pollen grain.’ Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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    What Are Pollen Cells

    In simple words, Pollination is defined as the transfer of Pollens from one flower to another, from the anther to the stigma. There are two more types of fertilization that occurs in plants – Cross-Pollination and Self-Pollination. Cross-Pollination is the transfer of pollen from the stigma of one flower to another. Self-Pollination is the transfer of pollen from the stigma of the same flower.

    Entry Of Pollen Tube Into The Embryo Sac

    • Irrespective of the entry of pollen tubes into the ovary, it enters the embryo sac through the micropyle.
    • The filiform apparatus guides the entry of pollen tubes into the cytoplasm of synergids.
    • The reproductive cells divide into two male gametes.
    • One gamete fuses with the egg in the embryo sac to form a zygote, while the other gamete fuses with two polar nuclei that form a food reserve for the seed called endosperm.
    • The double fusion of cells is characteristic of angiosperms, and is termed double fertilization.

    There are certain barriers that hinder the entry of pollen into the ovary. Visit to read about the incompatibility barriers and other topics.

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    Studying The Expression Profile Of Pollen

    Until recently, very few pollen-expressed genes were known, and of these only 23 had been identified in Arabidopsis . Because the sequence of the Arabidopsis genome is complete, it is now possible to investigate the gene-expression profile of pollen on a more global scale for the first time . Two different approaches were used to determine the overall gene-expression pattern of pollen: Affymetrix ATH1 8K GeneChips and serial analysis of gene expression . The fact that the ATH1 GeneChip does not represent the entire Arabidopsis genome but only 8,200 genes – 30% of the recent estimate of 28,000 genes in the Arabidopsis genome – suggests that more genes expressed in pollen remain to be identified. The SAGE approach is expected to overcome this problem, however, as it can detect expressed RNAs from genes that are not represented on the GeneChip, including genes that are not even predicted or annotated . Surprisingly, perhaps, the two approaches did give fairly similar overall views of pollen gene expression.

    Another interesting aspect of studying global pollen expression is the identification of RNA molecules differentially present or expressed in the different developmental stages of the pollen grain . These data allow investigation not only of which genes are expressed in pollen but also of the dynamics of their expression as pollen development proceeds.

    What Is Pollen In A Flower

    Pollen

    In pollen definition flowers, all Pollen Plant grains are not the same. They vary in size, shape, and characteristics, and this depends on the species of the plant. The structure of a Pollen is very simple. The grains have a double wall, and the thin inner wall is termed as endospore and is composed of cellulose. The thick outer wall is termed the exospore and consists of sporopollenin. Since the shape and size of endospore and exospore are variable, this is used by biologists to determine the species of the plant they belong to.

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    What Are Pollen Sacs

    Pollen sacs are cavities in the male reproductive system, anther, which produce pollen grains. The pollen sacs contain microspore mother cells which divide to produce four haploid microspores. The microspores further form the pollen grain.

    In angiosperms, there are usually four pollen sacs in each anther, whereas in gymnosperms there are a number of pollen sacs present which make up the male cone.

    The pollen sacs contain a number of archesporial cells which form the microspore mother cells. At first they are tightly bound together, but later get loosely arranged to help in the release of pollen grains.

    Pollen Grains: Things To Remember

    • Pollen grains refer to a powdery substance which is basically the male micro gametophytes of seeded plants, responsible for producing the male gametes.
    • The pollen grain comprises mainly 3 parts: intine, exine, and the inside of the cell filled with cytoplasm.
    • Pollination refers to the transfer of pollen grains from anther to the stigma of the flower.
    • There are three types of pollination: Autogamy, Xenogamy, and Geitonogamy.
    • The original color of pollen grains is white, however, it may seem yellow in various species.
    • Sexual Reproduction in Flowering plants is an important topic of the CBSE Class 12 Board Examination. Objective or long answer types of questions are framed from this section for 2 to 5 marks. The entire unit of reproduction has a weightage of 14 marks in the board examination.

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    What Is Pollen Grain

    Lets first understand what is Pollen grain. Pollen Plant refers to the mass of the microspores, which is the powdery product that is synthesized by the seed-bearing plants, and these are responsible for the production of male gametes as given in Pollen definition biology. The Pollens are transported by air, wind, water, insects, birds, and animals to the female plants for the purpose of fertilization.

    Wondering what is pollen in flowers? Pollens in flowers are also called microgametophytes, and they have a coating called sporopollenin. This coating is there to protect the gametophytes during transportation from stamens to pistil . In Pollen definition biology, after Pollen reaches the pistil, a certain type of tube is formed, which transports the stamen to the ovule. This phenomenon is also termed as Pollination, which is the reproductive system of plants.

    Department Of Plant Science Mcgill University Montreal Canada

    Pollination occurs when a pollen grain | 12 | SEXUAL REPRODUCTIO IN FLOWERING PLANTS | BIOLOGY |…

    Anja Geitmann

    • Book Title: Pollen and Pollen Tube Biology

    • Book Subtitle: Methods and Protocols

    • Editors: Anja Geitmann

    • Copyright Information: Springer Science+Business Media, LLC, part of Springer Nature 2020

    • Hardcover ISBN: 978-1-0716-0671-1

    • Number of Pages: XIII, 332

    • Number of Illustrations: 7 b/w illustrations, 90 illustrations in colour

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    What Does Pollen Contain

    Pollen grains consist of three parts. The centre cytoplasmic part is the one that is responsible for fertilization and is the source of the nuclei. The inner layer of the wall is called the intine, is composed of cellulose and hemicellulose. The walls outer layer is the most durable and is called the exine, and is exceptionally resistant. Even the treatment of the Pollen Plant with heat, strong winds, acids does not affect the outer layer. While the inner wall can break down easily, the exine layer is often preserved however, the quality varies with different environments.

    Structures And Analysis Of Gibberellins

    GAs are a major set of endogenous plant hormones, widely distributed throughout the plant kingdom and playing many key roles in higher plant growth and development, such as seed germination, stem elongation, the transition to flowering, pollen development, and fruit growth . As a class of tetracyclic diterpenoid carboxylic acids with either ent-gibberellane or 20-norent-gibberellane carbon skeletons, GAs comprise at least 136 highly similar endogenous analogs. Only a few of them have intrinsic biological activity, including GA1, GA3, GA4, GA5, GA6, and GA7, while GA1, GA3, and GA4 are the predominant bioactive GAs, but appear only at an ultra-trace level in the range of fmol to pmol per gram in plants, depending on the tissues and species . It is essential to know not only the concentrations of the bioactive forms of GAs, but also their precursors and metabolites, to provide important information of GA metabolism and function. However, it is a serious challenge to analyze, and especially to quantify, these complex and chemically similar ultra-trace GAs. The challenge is further increased by the poor detectability of GAs, which have no FLR and only weak UV absorbance, and in some cases by the limited availability of specific biological samples.

    Karina van der Linde, Virginia Walbot, in, 2019

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    Purpose Of The Structure

    The purpose of this simple pollen plant structure is to protect the genetic material from the external environment during the transportation of the pollen from the anther to the stigma. Not only the internal structure but the outer surface also contains wax and protein, which repels moisture and helps the pollen to mix with the stigma properly.

    What Is Pollination

    Nature Favors Production of Asymmetrical Pollen Grains

    Pollination is the act of transferring pollen grains from the male anther of a flower to the female stigma. The goal of every living organism, including plants, is to create offspring for the next generation. One of the ways that plants can produce offspring is by making seeds. Seeds contain the genetic information to produce a new plant.

    Flowers are the tools that plants use to make their seeds. The basic parts of the flower are shown in the diagram below.

    Seeds can only be produced when pollen is transferred between flowers of the same species. A species is defined a population of individuals capable of interbreeding freely with one another but because of geographic, reproductive, or other barriers, they do not interbreed with members of other species.

    Parts of a flower.

    This wasp is a specialist pollinator of Penstemon, which is the flower it is visiting, or rather sleeping in here. Photo by Dr. Jim Cane, USDA ARS Bee Biology and Systematics Laboratory, Logan, Utah.

    How does pollen get from one flower to another? Flowers must rely on vectors to move pollen. These vectors can include wind, water, birds, insects, butterflies, bats, and other animals that visit flowers. We call animals or insects that transfer pollen from plant to plant pollinators.

    This growth can result in:

    Plants can be:

    • Self-pollinating – the plant can fertilize itself or,
    • Cross-pollinating – the plant needs a vector to get the pollen to another flower of the same species.

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    What Is Pollen

    What is Pollen? In simple words, pollen can be defined as a fine or a coarse powder, which consists of microgemetophytes and produces the male gametes or the sperm cells. Palynology is the branch of Biology, which mainly deals with the study of pollens and their properties.

    Pollen grains are microscopic structures, which bear androecium a male reproductive organ of a flower. The interior section of pollen grain contains cytoplasm along with the tube cell, which converts into a pollen tube and the generative cell releases the sperm nuclei. Read More: Pollination

    Pollen grains are microscopic structures varying in their size and structure. The size of pollen grains generally varies with the species. Overall, the exact size of pollen grain ranges between three and two hundred micrometres or microns. The shape of the pollen grain is commonly found in round, ovule, triangular, disc or in a bean-shape with a smooth to spiky texture. The natural colour of pollen grains are white, which may also vary depending on the plant species. Some are yellow in colour, or orange, or cream and so on. Pollen grains consist of three parts:

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