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Chapter 38

Chapter 38. Plant Reproduction and Biotechnology. Unique features of the angiosperm life cycle: 1. flowers, 2. double fertilization, and 3. fruits. Diploid (2 n ) sporophytes produce spores by meiosis; these grow into haploid ( n ) gametophytes

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Chapter 38

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  1. Chapter 38 Plant Reproduction and Biotechnology

  2. Unique features of the angiosperm life cycle: 1. flowers, 2. double fertilization, and 3. fruits • Diploid (2n) sporophytes produce spores by meiosis; these grow into haploid (n) gametophytes • Gametophytes produce haploid (n) gametes by mitosis; fertilization of gametes produces a sporophyte • Sporophyte is the dominant generation, the gametophytes are reduced

  3. Germinated pollen grain (n) (male gametophyte) Anther Ovary Pollen tube Ovule Embryo sac (n) (female gametophyte) FERTILIZATION Egg (n) Sperm (n) Zygote (2n) Mature sporophyte plant (2n) Key Seed Haploid (n) Diploid (2n) Germinating seed Seed Embryo (2n) (sporophyte) Simple fruit (b) Simplified angiosperm life cycle

  4. Flower Structure and Function • Receptacle- where flowers attach to the stem • Flowers consist of four floral organs: sepals, petals, stamens, and carpels Stigma Anther Carpel Stamen Style Filament Ovary Sepal Petal Receptacle (a) Structure of an idealized flower

  5. Flower Structure and Function • Stamen: filament topped by an anther with pollen sacs that produce pollen Stigma Anther Carpel Stamen Style Filament Ovary Sepal Petal Receptacle (a) Structure of an idealized flower

  6. Flower Structure and Function • Carpel: has a long style with a stigma on which pollen may land. At the base of the style is an ovary containing one or more ovules Stigma Anther Carpel Stamen Style Filament Ovary Sepal Petal Receptacle (a) Structure of an idealized flower

  7. Complete flowers contain all four floral organs • Incomplete flowers lack one or more floral organs, for example stamens or carpels

  8. Abiotic Pollination by Wind Hazel staminate flowers (stamens only) Hazel carpellate flower (carpels only)

  9. (b) (a) Development of a male gametophyte (in pollen grain) Development of a female gametophyte (embryo sac) Microsporangium (pollen sac) Megasporangium (2n) Microsporocyte (2n) Ovule Megasporocyte (2n) MEIOSIS Integuments (2n) Micropyle 4 microspores (n) Surviving megaspore (n) Each of 4 microspores (n) MITOSIS Ovule 3 antipodal cells (n) Male gametophyte Generative cell (n) Female gametophyte (embryo sac) 2 polar nuclei (n) 1 egg (n) Nucleus of tube cell (n) Integuments (2n) 2 synergids (n) 20 µm Ragweed pollen grain Embryo sac 100 µm 75 µm

  10. (a) Development of a male gametophyte (in pollen grain) Development of Male Gametophytes in Pollen Grains Microsporangium (pollen sac) Microsporocyte (2n) • Pollen develops from microspores within the microsporangia, or pollen sacs, of anthers MEIOSIS 4 microspores (n) Each of 4 microspores (n) MITOSIS Male gametophyte Generative cell (n) Nucleus of tube cell (n) 20 µm Ragweed pollen grain 75 µm

  11. (a) Development of a male gametophyte (in pollen grain) Development of Male Gametophytes in Pollen Grains Microsporangium (pollen sac) Microsporocyte (2n) In pollination- a pollen grain produces a pollen tube that grows down into the ovary and discharges sperm near the embryo sac MEIOSIS 4 microspores (n) Each of 4 microspores (n) MITOSIS Male gametophyte Generative cell (n) Nucleus of tube cell (n) 20 µm Ragweed pollen grain 75 µm

  12. (a) Development of a male gametophyte (in pollen grain) Development of Male Gametophytes in Pollen Grains Microsporangium (pollen sac) Microsporocyte (2n) The pollen grain consists of the two-celled male gametophyte and the spore wall MEIOSIS 4 microspores (n) Each of 4 microspores (n) MITOSIS Male gametophyte Generative cell (n) Nucleus of tube cell (n) 20 µm Ragweed pollen grain 75 µm

  13. (b) Development of a female gametophyte (embryo sac) Development of Female Gametophytes (Embryo Sacs) Megasporangium (2n) • Within an ovule, megaspores are produced by meiosis and develop into embryo sacs, the female gametophytes Ovule Megasporocyte (2n) MEIOSIS Integuments (2n) Micropyle Surviving megaspore (n) MITOSIS Ovule 3 antipodal cells (n) Female gametophyte (embryo sac) 2 polar nuclei (n) 1 egg (n) Integuments (2n) 2 synergids (n) Embryo sac 100 µm

  14. Pollination- the transfer of pollen from an anther to a stigma Pollination by Bees Common dandelion under normal light Common dandelion under ultraviolet light

  15. Pollination by Moths and Butterflies Anther Stigma Moth on yucca flower

  16. Pollination by Flies Fly egg Blowfly on carrion flower

  17. Pollination by Birds Hummingbird drinking nectar of poro flower

  18. Pollination by Bats Long-nosed bat feeding on cactus flower at night

  19. Animation: Plant Fertilization Double Fertilization Pollen grain Stigma • After landing on a receptive stigma, a pollen grain produces a pollen tube that extends between the cells of the style toward the ovary Pollen tube 2 sperm Style Ovary Ovule Polar nuclei Micropyle Egg

  20. Double fertilization results from the discharge of two sperm from the pollen tube into the embryo sac Ovule Polar nuclei Egg Synergid 2 sperm

  21. One sperm fertilizes the egg, and the other combines with the polar nuclei, giving rise to the triploid (3n) food-storing endosperm Endosperm nucleus (3n) (2 polar nuclei plus sperm) Zygote (2n) (egg plus sperm)

  22. Seed Development, Form, and Function • After double fertilization, each ovule develops into a seed • The ovary develops into a fruit enclosing the seed(s) Endosperm Development • Endosperm development usually precedes embryo development • It stores nutrients that can be used by the seedling or the food reserves are exported to the cotyledons

  23. Embryo Development Ovule The first mitotic division of the zygote splits the fertilized egg into a basal cell and a terminal cell Endosperm nucleus Integuments Zygote Zygote Terminal cell Basal cell Proembryo Suspensor Basal cell Cotyledons Shoot apex Animation: Seed Development Root apex Seed coat Endosperm Suspensor

  24. Structure of the Mature Seed Ovule Endosperm nucleus • The embryo and its food supply are enclosed by a hard, protective seed coat • The seed enters a state of dormancy Integuments Zygote Zygote Terminal cell Basal cell Proembryo Suspensor Basal cell Cotyledons Shoot apex Root apex Seed coat Endosperm Suspensor

  25. Cotyledons- become the first leaves • Hypocotyl- embryonic axis • Radicle- embryonic root • Epicotyl- region above the cotyledons Seed coat Epicotyl Hypocotyl Radicle (a) Common garden bean, a eudicot with thick cotyledons Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle (b) Castor bean, a eudicot with thin cotyledons Pericarp fused with seed coat Scutellum (cotyledon) Endosperm Coleoptile Epicotyl Hypocotyl Coleorhiza Radicle (c) Maize, a monocot

  26. Seed coat Epicotyl Hypocotyl Radicle (a) Common garden bean, a eudicot with thick cotyledons

  27. Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle (b) Castor bean, a eudicot with thin cotyledons

  28. Pericarp fused with seed coat Scutellum (cotyledon) Endosperm Coleoptile Epicotyl Hypocotyl Coleorhiza Radicle (c) Maize, a monocot

  29. Seed Dormancy Increases the chances that germination will occur at a time and place most advantageous to the seedling The breaking of seed dormancy often requires environmental cues, such as temperature or lighting changes

  30. Seed Germination and Seedling Development Foliage leaves Cotyledon Epicotyl Hypocotyl Cotyledon Cotyledon Hypocotyl Hypocotyl Radicle Seed coat (a) Common garden bean

  31. Germination depends on imbibition, the uptake of water due to low water potential of the dry seed • The radicle emerges first and then the shoot Foliage leaves Coleoptile Coleoptile Radicle (b) Maize

  32. Fruit Form and Function • A fruit develops from the ovary. It protects the enclosed seeds and aids in seed dispersal by wind or animals • Dry fruit- ovary dries out at maturity • Fleshy fruit- ovary becomes thick, soft, and sweet at maturity Animation: Fruit Development

  33. Ovary Stamen • Simple, a single or several fused carpels Stigma Ovule Pea flower Seed Pea fruit (a) Simple fruit

  34. Carpels Stamen • Aggregate, a single flower with multiple separate carpels Raspberry flower Carpel (fruitlet) Stigma Ovary Stamen Raspberry fruit (b) Aggregate fruit

  35. Flower • Multiple, a group of flowers called an inflorescence Pineapple inflorescence Each segment develops from the carpel of one flower Pineapple fruit (c) Multiple fruit

  36. Stigma Style Petal An accessory fruit contains other floral parts in addition to ovaries Stamen Sepal Ovary (in receptacle) Ovule Apple flower Remains of stamens and styles Sepals Seed Receptacle Apple fruit (d) Accessory fruit

  37. Dispersal by Water Coconut

  38. Dispersal by Wind Winged seed of Asian climbing gourd Dandelion “parachute” Winged fruit of maple Tumbleweed

  39. Dispersal by Animals Barbed fruit Seeds in feces Seeds carried to ant nest Seeds buried in caches

  40. Plants reproduce sexually, asexually, or both • Many angiosperm species reproduce both asexually and sexually • What are the advantages and disadvantages of asexual versus sexual reproduction?

  41. Mechanisms of Asexual Reproduction • Fragmentation- separation of a parent plant into parts that develop into whole plants • In some species, a parent plant’s root system gives rise to adventitious shoots that become separate shoot systems • Apomixis is the asexual production of seeds from a diploid cell

  42. Mechanisms That Prevent Self-Fertilization • Dioecious species have staminate and carpellate flowers on separate plants (a) Sagittaria latifolia staminate flower (left) and carpellate flower (right)

  43. Others have stamens and carpels that mature at different times or are arranged differently Styles Stamens Styles Stamens Thrum flower Pin flower (b) Oxalis alpina flowers • The most common is self-incompatibility, a plant’s ability to reject its own pollen

  44. Vegetative Propagation (asexual reproduction) and Agriculture Clones from Cuttings • A stem is cut and produces adventitious roots Grafting • A twig or bud can be grafted onto a plant of a closely related species or variety Test-Tube Cloning and Related Techniques • Transgenic plants are genetically modified (GM) to express a gene from another organism

  45. (a) Undifferentiated carrot cells (b) Differentiation into plant

  46. Humans modify crops by breeding and genetic engineering • Hybridization is common in nature and has been used by breeders to introduce new genes

  47. Plant Biotechnology and Genetic Engineering Reducing World Hunger and Malnutrition • Genetically modified plants may increase the quality and quantity of food worldwide • Transgenic crops have been developed that: • Produce proteins to defend them against insect pests • Tolerate herbicides • Resist specific diseases

  48. “Golden Rice” is a transgenic variety being developed to address vitamin A deficiencies among the world’s poor Genetically modified rice Ordinary rice

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