Pre fertilization structures in plants.. (Flower structure and male and female gametes production)

Pre fertilization structures in plants.. (Flower structure and male and female gametes production)

• 1.
  Sexual Reproduction in Flowering plants. D.Sreekanth.M.Sc.,NET, TS/AP-SET, (Ph.D) Department of Botany, Osmani University, Hyderabad. Email id: shreekanthdasari@gmail.com
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  Lesson Outline  Introduction:Sexual Reproduction  Flowering Plants  Post fertilization: structures and events  Double fertilization  Post fertilization: structures and events.
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  Reproduction  Reproduction isthe creation of “new individuals” from existing individuals.
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  Two Types ofReproduction  Sexual – involves sex cells (egg, sperm)  Asexual – does not involve sex cells
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  In asexual reproduction, the parentcell is SINGLE AND DIVIDING. (ex. amoeba, hydra, fungi, bacteria, etc.)
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  In sexual reproduction, theoffspring are genetically identical (exact clones) to their parents. (ex. humans, elephants, dogs, fishes, plants, etc.)
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  Sexual Reproduction  Involvesunion of gametes  Gametes = sperm (male) + egg (female)  Trivia: The egg is the largest cell in the human body while the sperm is the smallest.
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  Sexual Reproduction  Sperm– mobile and small  Egg – immobile and large  During fertilization, they unite (n + n) to form a diploid (2n) zygote (fertilized egg)
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  Flowering Plants  Comprises90% of plant species  Classified as either: 1. Angiosperms – have seeds enclosed in ovary 2. Anthophytes – plants that produce flowers. They have an ovary that’s part of the flower
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  Pre fertilisation Fertilisation Post fertilisation SexualReproduction
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  Pre fertilization
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  What is the Reproductiveorgan in plants..?
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  Flowers  Reproductive organs/structuresof a plant  Most flowers are hermaphrodites (contains both male and female sex organs)
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  The Flower – Whatis it?
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  • thus, aflower is a specialized shoot that: 1. is determinate (vs. indeterminate) 2. has a modified stem with compressed internodes 3. possesses modified leaves with various functions, these determined by gene arrays (e.g., ABC model) 4. often clustered in an inflorescence (larger branch) The Flower — What is it?
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  Parts of aFlower  Corolla  Calyx  Stamen (male)  Pistil (female)  Receptacle  Peduncle (Be sure to be able to memorize and label each part)
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  Accessory Parts –function mainly for support, protection and attraction • Corolla • Calyx • Receptacle • Peduncle
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  Calyx  Comprises of sepals(typically green)  Leaf-like  Function: Protect the flower when it was still young sepal
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  Corolla  Comprises ofthe petals  Have various shapes, sizes, and colors  Function: protection, attraction
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  Receptacle  Also calledtorus  Function: Supports the entire flower (base of the flower) receptacle calyx
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  Peduncle  Also calledstalk  Function: Connects the flower to the branch or stem. peduncle
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  Reproductive Parts –for reproduction; main parts of a flower 1. Stamen (male) 2. Pistil (female)
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  Stamen  The malereproductive organ  Collectively called androecium (collective noun)  Composed of two parts: 1. Anther 2. Filament
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  Anther  Expanded lobular structureat the end of the filament  Function: Produces pollen (male sex cell)
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  Filament  Function: Stalk thatsupports and holds the anther
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   Bilobed  Dithecous longitudinal groove  four-sided (tetragonal)  four microsporangia (pollen sacs) Anther: Structure four microsporangia
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   Epidermis  Endothecium Middle layers  Tapetum  Sporogenous tissue Anther wall layers
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  Epidermis: one cell thick. Function: dehiscence of anther.  Stomium: present between 2 pollen sacs.  Anther dehiscence at this stomium region. Anther wall layers
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  Endothesium: Below the epidermis. one cell thick.  fibrous cellulose thickenings + little pectin.  Function:at maturity these cells loose the water and helps in dehiscence of anther. Anther wall layers
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  Middle layers: Below the endothecium. Function:at maturity these cells degenerate.  helps in dehiscence of anther and protection of anther. Anther wall layers
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  Tapetum: Inner most layer. Surroundsthe sprogenous tissue. Cells are multinucleate and polyploid. Contain ubisch bodies. Ubisch bodies secretes- sporopollenin.  Function: Nourishes the developing pollen grains. Anther wall layers
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  Microsporogenesis sporogenous tissue sporogenous cell(2n) microspore tetrad (n) Microspore tetrad/pollen graintetrad (n) Microspores/pollen grains (n) Formation and differentiation of microspore is called microsporogenesis.
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  Structure of Pollen/microspore
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  Resistant to  Hightemperatures  Strong acids and alkali  Enzymes  fossils because of the presence of sporopollenin Sporopollennin
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  In over 60per cent of angiosperms, pollen grains are shed at this 2-celled stage
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   severe allergies Bronchial afflictions  chronic respiratory disorders– asthma, bronchitis  Parthenium or carrot grass- Afflictions, asthma, bronchitis Pollen allergy Pollen grains
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   rich innutrients  pollen tablets as food supplements  tablets and syrups  to increase the performance of athletes and race horses Pollen grains are
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   pollen grainsof a large number of species are stored for years in liquid nitrogen (-196ºC)… through cryopreservation. Pollen banks
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  41 Structure of aPollen grain The pollen grains represent the male gametophytes. Viability of pollen grains depends on temperature and humidity. Viable from few mins to several months. – few mins (rice, wheat) to few months (Solanacae), Rosaceae, Leguminoseae
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  The female reproductive organ/Unit (Pistil)
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  Pistil or carpel The female reproductive organ  Collectively called gynoecium (collective noun)  Composed of three parts: 1. Stigma 2. Style 3. Ovary ovarystyle CARPEL (female reproductive part) stigma
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  Stigma  Swollen tipof the pistil  Function:  Covered by sticky substance for pollen grains to adhere (stick).  specialized for receiving pollen grains. stigma Pollen grains (purple dots)
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  Style  Function: Long, slendertube that connects the stigma to the ovary  Acts as a conveyor (carrier from one place to another) of pollen grains style
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  Ovary  Enlarged basal portionof the pistil  Function: Houses the ovule  The ovule houses the egg cell
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  Ovary In cross section,internal parts of the ovary can be seen: Carpel Locule Ovule Funiculus Placenta
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  Ovary Carpel – segment or partitionthat comprises an ovary Ovary wall – supports the ovary Ovary with 3 carpels
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  Ovary Locule – space orcavity within the carpel An ovary with 3 carpels has also 3 locules room-like locules
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  ovules (2 ovules per locule) Cross-section ofa plant ovary carpel
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  Ovary Ovary core – solidstructure at the center Placenta – the edge of the core; nourishes the egg core (yellow); placenta (green) Visual representation core placenta placenta core
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  Ovary Finuculus – short stalkthat connects the ovule and placenta finiculus finiculus
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  Ovary Ovule – produces the egg ovule ovule ovule
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  Types in carpel 3examples Carpels not fused 1. Monocarpic 2. MULTICARPELLARY. a.Apocarpic. b.Syncarpic
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  1 floral ‘leaf’in gynoecium This gynoecium is monocarpic (one carpel) Folded ‘leaf’ 1 carpel = 1 pistil Monocarpic
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  • If 9‘leaves’ in one flower each separately forms carpels, • then the flower has 9 carpels and 9 pistils, • gynoecium is apocarpic (separate carpels) Caltha palustris - Marsh marigold 9 fruits (pistils) from 1 flower Gynoecium is apocarpic with 9 carpels or 9 pistils Multicarpellary– Apocarpous
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  3 floral ‘leaves’in gynoecium fuse This gynoecium is syncarpic This gynoecium is syncarpic Multicarpellary----Syncarpic 3 carpels = 1 pistil 3 styles 3 carpels = 1 pistil 1 style
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  Structure of ovule.. Ovule (Megasporangium)
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  Cross-section of anovule The ovule has the following parts: 1. Integument - 2 layer protective coat 2. Nucellus – mass of tissue consisting of meristematic (dividing) cells 3. Funiculus- attaches ovule to placenta. 4. Embryo sac – contains the egg. 5. Micropyle- 6. Chalaza-
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  types of ovules..
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  61  (1) Orthotropous: The micropyle, chalaza and funicle are in a straight line. This is the most primitive type of ovule e.g., Piper, Polygonum, Cycas. - A  (2) Anatropous : The ovule turns at 180 angle. Thus it is inverted ovule. Micropyle lies close to hilum or at side of hilum e.g, found in 90% of angiosperm families. B  (3) Campylotropous : Ovule is curved more or less at right angle to funicle. Micropylar end is bend down slightly e.g., in members of Leguminosae, Cruciferae. D  (4) Hemianatropous : Ovule turns at 90 angle upon the funicle or body of ovule and is at right angle to the funicle e.g., Ranunculus. C  (5) Amphitropous : Ovule as well as embryo sac is curved like horse shoe e.g, Lemna, Poppy, Alisma. E  (6) Circinotropous : The ovule turns at more than 360 angle, so funicle becomes coiled around the ovule e.g., Opuntia (Cactaceae), Plumbaginaceae. F
• 62.
  Development of Gametophytes (Egg)Two Stages 1. Megasporogenesis (genesis = beginning/creation) – creation of megaspores 2. Megagametogenesis – creation of the gametes (egg)
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  Development of Gametophytes (Egg) 1.Megasporogenesis A. Ovule produces megaspore mother cell (2n). B. Megaspore mother cell (2n) produces 4 megaspores (n) via a two- time meiosis. C. 3 megaspores die and only one is left to continue. 2n n n meiosis n n meiosis n n meiosis
• 64.
  Development of Gametophytes (Egg) 1.Megagametogenesis A. The surviving megaspore divides via mitosis 3 times, forming 8 haploid (n) cells) n megaspore n n n n n n nnnnnnnn mitosis mitosis mitosis mitosismitosismitosismitosis 8 haploid (n) cells
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  Egg Development inOvule B. Among the eight cells:  3 cells migrate near the micropyle. The one at the center becomes the egg while the other two becomes the synergid cells.  The other 3 migrate on the opposite pole and become antipodal cells.  The remaining 2 cells are naked (no membrane) and remains at the center to become the polar nuclei. micropyle egg synergidsynergid antipodal polar nuclei
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  Egg (Embryosac)Development in Ovule C.These 8 cells form the inside of the embryo sac and are ready to be fertilized by a pollen (from the male).
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  67 Embryo sac development1
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  68 Pollination
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  Pollination Transfer of pollenfrom the anther to the stigma of a flower of the same species
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  Pollination Self pollination • Transferof pollen from an anther to a stigma of the same plant Cross pollination • Transfer of pollen from the anther to the stigma of a different plant of the same species
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  71 Pollination Transfer of pollengrains from anther to stigma( pistil) Self pollination Same flower/ different flower of same plant Autogamy Pollination in the same flower Chasmogamy Flowers open, synchrony in pollen release and stigma Close arrangement Cleistogamy flowers which do not open at all Geitonogamy Different flowers same plant. Cross- pollination Two flowers of different plants of same species Xenogamy Viola (common pansy), Oxalis, and Commelina produce two types of flowers chasmogamous, cleistogamous
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  Biotic pollination agents:Pollination by animals (organisms)  80% of all pollination is biotic  Entomophily – pollination by insects  Butterflies (psychophily):  Moths (phalaenophily):  Flies (sapromyiophily)  Birds (ornithophily):  Bats (cheiropterophily): Pollination
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  Abiotic pollination: Pollinationby non-animal factors Amenophily Pollination by wind (98% of abiotic pollination) Hydrophily Pollination by water (aquatic plants) A. epihydrophilly- mediated by surface water= Vallisneria. B. hypohydrophilly- bottom water- zostero. Pollination Vallisneria, hydrilla- freshwater forms Zostera- marine Vallisneria- water surface Sea grasses- inside water Water hyacinth, water lilly – wind and insects
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  Petals brightly coloured, scentedwith nectaries Small amounts of sticky pollen Anthers inside petals Stigmas sticky, inside petals Adaptations for animal (insect) pollination
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   light  non-sticky well-exposed stamens  large often-feathery stigma  single ovule in each ovary  Inflorescence  common in grasses Wind pollination
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   limited toabout 30 genera  mostly monocotyledons  distribution is limited because of the need for water for transport of male gametes  Vallisneria, hydrilla- freshwater forms  Zostera- marine  Vallisneria- water surface  Sea grasses- inside water  Water hyacinth, water lilly – wind and insects  long, ribbon like pollen  Pollen grains have mucilaginous covering  not colourful  Do not produce nectar Water pollination
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  Colour and/fragrance foul odours Nectarand pollen grains-floral rewards providing safe places to lay eggs Amorphophallus moth and the Yucca relationship Animal pollination
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  Outbreeding Devices
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   To overcomeinbreeding depression  Pollen release and stigma receptivity not synchronized  Anther and stigma placed at different positions  Self incompatibility  Production of unisexual flowers  Monoecious/dioecious condition Outbreeding Devices
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   Outbreeding devices: The following six types of devices promote and ensure outbreeding through cross pollination:  UNISEXUALITY (Dicliny): Flowers are unisexual or diclinous. Plants may be monoecious (eg. Maize, castor) or dioecious (eg. Mulberry, papaya, date palm).
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   Outbreeding devices: DICHOGAMY: (Gk-dicha- in two, gamos- marriage)  Here in a bisexual flower, anthers and stigmas nature at different times, so that self pollination is inhibited.  Eg. Clerodendron, Salvia, Sunflower, Rose, Magnolia, Gloriosa etc. protandry - male first protogyny - female first
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   Outbreeding devices: HETEROSTYLY: Flower have different types of height of styles and stamens.  Eg. Jasmine, Primrose, Lythyrsus, Oxalis.
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   Outbreeding devices: SELF – STERILITY- Pollen grains of one flower are incapable of growing over the stigma of same flower due to the presence of similar sterile genes. Eg. Crucifers, Potato, Tobacco, Gramineae, Orechidaceae.
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   Outbreeding devices:  HERKOGAMY:They are mechanical devices that prevent self pollination and favour cross pollination even in homogamous flowers. Ex; Hibiscus, Gloriosa.
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  Outbreeding devices: PREPOTENCY: Pollengrains of one flower grow more rapidly over the stigma of another flower as compared to the same flower.  Eg. Apple, Grape.
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   Emasculation female parentbears bisexual flowers, removal of anthers from the flower bud before the anther dehisces using a pair of forceps.  Bagging Emasculated flowers have to be covered with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollen. Artificial Hybridisation
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   When thestigma of bagged flower attains receptivity, mature pollen grains collected from anthers of the male parent are dusted on the stigma, and the flowers are rebagged, and the fruits allowed to develop.  unisexual flowers, no emasculation. The female flower buds are bagged before the flowers open.  When the stigma becomes receptive, pollination is carried out using the desired pollen and the flower rebagged. Artificial Hybridisation
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  Emasculation-removal of anthersfrom the flower bud before the dehiscence of anther
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  Pollen- Pistil Interaction:
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  Pollen- Pistil Interaction: acontinuous dialogue between pollen grain and the pistil mediated by chemical components of the pollen and the pistil.  wrong type (incompatible). Suitable type (compatible) of pollen compatible pollen grains germinate on the stigma pollen tube through germ tube
• 93.
  Pollen and stigmaincompatibility There can be dozens of alleles of the S-gene. If a pollen grain has an allele that matches an allele of the stigma upon which it lands, then the pollen tube fails to grow. This system prevents self-fertilization AND fertilization from close relatives.
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  94  Germination- formationof pollen tube through germ pore- content move to pollen tube- through stigma, style reaches ovary  pollen grains - two-celled condition (a vegetative cell and a generate cell)- the generative cell divides and forms the two male gametes during the growth of pollen tube in the stigma.  three-celled condition, pollen tubes carry the two male gametes from the beginning.  Pollen tube, after reaching the ovary, enters the ovule through the micropyle and then enters one of the synergids through the filiform apparatus  Interaction is important in plant breeding- for superior plant development
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  The end pre fertilizationstructures.