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

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: [email protected]

2. Lesson Outline Introduction: Sexual Reproduction Flowering Plants Post fertilization: structures and events Double fertilization Post fertilization: structures and events.

3. Reproduction Reproduction is the creation of “new individuals” from existing individuals.

4. Two Types of Reproduction Sexual – involves sex cells (egg, sperm) Asexual – does not involve sex cells

5. In asexual reproduction, the parent cell is SINGLE AND DIVIDING. (ex. amoeba, hydra, fungi, bacteria, etc.)

6. In sexual reproduction, the offspring are genetically identical (exact clones) to their parents. (ex. h umans, elephants, dogs, fishes, plants, etc.)

7. Sexual Reproduction Involves union of gametes Gametes = sperm (male) + egg (female) Trivia: The egg is the largest cell in the human body while the sperm is the smallest.

8. Sexual Reproduction Sperm – mobile and small Egg – immobile and large During fertilization, they unite (n + n) to form a diploid (2n) zygote (fertilized egg)

9. Flowering Plants Comprises 90% of plant species Classified as either: Angiosperms – have seeds enclosed in ovary Anthophytes – plants that produce flowers. They have an ovary that’s part of the flower

10. Pre fertilisation Fertilisation Post fertilisation Sexual Reproduction

11. Pre fertilization

12. What is the Reproductive organ in plants..?

13. Flowers Reproductive organs/structures of a plant Most flowers are hermaphrodites (contains both male and female sex organs)

14. The Flower – What is it?

15. thus, a flower is a specialized shoot that: is determinate (vs. indeterminate) has a modified stem with compressed internodes possesses modified leaves with various functions, these determined by gene arrays (e.g., ABC model) often clustered in an inflorescence (larger branch) The Flower — What is it?

16. Parts of a Flower Corolla Calyx Stamen (male) Pistil (female) Receptacle Peduncle (Be sure to be able to memorize and label each part)

17. Accessory Parts – function mainly for support, protection and attraction Corolla Calyx Receptacle Peduncle

18. Calyx Comprises of sepals (typically green) Leaf-like Function : Protect the flower when it was still young sepal

19. Corolla Comprises of the petals Have various shapes, sizes, and colors Function : protection, attraction

20. Receptacle Also called torus Function : Supports the entire flower (base of the flower) receptacle calyx

21. Peduncle Also called stalk Function : Connects the flower to the branch or stem . peduncle

22. Reproductive Parts – for reproduction; main parts of a flower Stamen (male) Pistil (female)

23. Stamen The male reproductive organ Collectively called androecium (collective noun) Composed of two parts: Anther Filament

24. Anther Expanded lobular structure at the end of the filament Function : Produces pollen (male sex cell)

25. Filament Function : Stalk that supports and holds the anther

26. Bilobed Dithecous longitudinal groove four-sided (tetragonal) four microsporangia (pollen sacs) Anther: Structure four microsporangia

27. Epidermis Endothecium Middle layers Tapetum Sporogenous tissue Anther wall layers

28. Epidermis: one cell thick. Function: dehiscence of anther. Stomium : present between 2 pollen sacs. Anther dehiscence at this stomium region. Anther wall layers

29. 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

30. Middle layers: Below the endothecium . Function: at maturity these cells degenerate. helps in dehiscence of anther and protection of anther. Anther wall layers

31. Tapetum : Inner most layer. Surrounds the sprogenous tissue. Cells are multinucleate and polyploid . Contain ubisch bodies . Ubisch bodies secretes- sporopollenin . Function: Nourishes the developing pollen grains. Anther wall layers

32. Microsporogenesis Formation and differentiation of microspore is called microsporogenesis .

33. Structure of Pollen/microspore

34. Resistant to High temperatures Strong acids and alkali Enzymes fossils because of the presence of sporopollenin Sporopollennin

35. In over 60 per cent of angiosperms, pollen grains are shed at this 2-celled stage

36. severe allergies Bronchial afflictions chronic respiratory disorders– asthma, bronchitis Parthenium or carrot grass- Afflictions, asthma, bronchitis Pollen allergy Pollen grains

37. rich in nutrients pollen tablets as food supplements tablets and syrups to increase the performance of athletes and race horses Pollen grains are

38. pollen grains of a large number of species are stored for years in liquid nitrogen (-196 º C)… through cryopreservation. Pollen banks

39. 41 Structure of a Pollen 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

40. The female reproductive organ/Unit (Pistil)

41. Pistil or carpel The female reproductive organ Collectively called gynoecium (collective noun) Composed of three parts: Stigma Style Ovary ovary style CARPEL (female reproductive part) stigma

42. Stigma Swollen tip of the pistil Function : Covered by sticky substance for pollen grains to adhere (stick). specialized for receiving pollen grains . stigma Pollen grains (purple dots)

43. Style Function : Long, slender tube that connects the stigma to the ovary Acts as a conveyor (carrier from one place to another) of pollen grains style

44. Ovary Enlarged basal portion of the pistil Function : Houses the ovule The ovule houses the egg cell

45. Ovary In cross section, internal parts of the ovary can be seen: Carpel Locule Ovule Funiculus Placenta

46. Ovary Carpel – segment or partition that comprises an ovary Ovary wall – supports the ovary Ovary with 3 carpels

47. Ovary Locule – space or cavity within the carpel An ovary with 3 carpels has also 3 locules r oom-like locules

48. locule 1 locule 2 locule 3 o vules (2 ovules per locule ) Cross-section of a plant ovary carpel

49. Ovary Ovary core – solid structure at the center Placenta – the edge of the core; nourishes the egg c ore (yellow); placenta (green) Visual representation c ore placenta placenta core

50. Ovary Finuculus – short stalk that connects the ovule and placenta ovule finiculus finiculus

51. Ovary Ovule – produces the egg ovule ovule ovule

52. Types in carpel 3 examples Carpels not fused 1. Monocarpic 2. MULTICARPELLARY. Apocarpic . Syncarpic

53. 1 floral ‘leaf’ in gynoecium This gynoecium is monocarpic (one carpel) Folded ‘leaf’ 1 carpel = 1 pistil Monocarpic

54. 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

55. 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

56. Structure of ovule.. Ovule ( Megasporangium )

57. Cross-section of an ovule The ovule has the following parts: Integument - 2 layer protective coat Nucellus – mass of tissue consisting of meristematic (dividing) cells Funiculus - attaches ovule to placenta. Embryo sac – contains the egg. Micropyle - Chalaza -

58. types of ovules..

59. 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

60. Development of Gametophytes (Egg) Two Stages Megasporogenesis (genesis = beginning/creation) – creation of megaspores Megagametogenesis – creation of the gametes (egg)

61. Development of Gametophytes (Egg) Megasporogenesis Ovule produces megaspore mother cell (2n). Megaspore mother cell (2n) produces 4 megaspores (n) via a two-time meiosis. 3 megaspores die and only one is left to continue. 2n n n meiosis n n meiosis n n meiosis

62. Development of Gametophytes (Egg) Megagametogenesis The surviving megaspore divides via mitosis 3 times, forming 8 haploid (n) cells) n megaspore n n n n n n n n n n n n n n mitosis mitosis mitosis mitosis mitosis mitosis mitosis 8 haploid (n) cells

63. Egg Development in Ovule 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 synergid synergid antipodal polar nuclei

64. Egg ( Embryosac )Development in Ovule These 8 cells form the inside of the embryo sac and are ready to be fertilized by a pollen (from the male).

65. 67 Embryo sac development 1

66. 68 Pollination

67. Pollination Transfer of pollen from the anther to the stigma of a flower of the same species

68. Pollination Self pollination Transfer of 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

69. 71 Viola ( common pansy) , Oxalis, and Commelina produce two types of flowers chasmogamous , cleistogamous

70. 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 NM Spirit

71. Abiotic pollination: Pollination by 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 NM Spirit Vallisneria , hydrilla - freshwater forms Zostera - marine Vallisneria - water surface Sea grasses- inside water Water hyacinth, water lilly – wind and insects

72. Petals brightly coloured, scented with nectaries Small amounts of sticky pollen Anthers inside petals Stigmas sticky , inside petals Adaptations for animal (insect) pollination

73. light non-sticky well-exposed stamens large often-feathery stigma single ovule in each ovary Inflorescence common in grasses Wind pollination

74. limited to about 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

75. Colour and/fragrance foul odours Nectar and pollen grains-floral rewards providing safe places to lay eggs Amorphophallus moth and the Yucca relationship Animal pollination

76. Outbreeding Devices

77. To overcome inbreeding 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

78. 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).

79. 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

80. Outbreeding devices: HETEROSTYLY: Flower have different types of height of styles and stamens. Eg . Jasmine, Primrose, Lythyrsus , Oxalis.

81. 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 .

82. Outbreeding devices: HERKOGAMY: They are mechanical devices that prevent self pollination and favour cross pollination even in homogamous flowers. Ex; Hibiscus, Gloriosa .

83. Outbreeding devices: PREPOTENCY: Pollen grains of one flower grow more rapidly over the stigma of another flower as compared to the same flower. Eg . Apple, Grape.

84. Emasculation female parent bears 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

85. When the stigma 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

86. Emasculation-removal of anthers from the flower bud before the dehiscence of anther

87. Pollen- Pistil Interaction:

88. Pollen- Pistil Interaction: a continuous 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

89. Pollen and stigma incompatibility 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 .

90. 94 Germination - formation of 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

91. The end pre fertilization structures.