BIOLOGY. Reproduction of flowering Plants CAMPBELL. Reece Urry Cain Wasserman Minorsky Jackson

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1 CAMPBELL BIOLOGY TENTH EDITION Reece Urry Cain Wasserman Minorsky Jackson 38 Reproduction of flowering Plants Lecture Presentation by Nicole Tunbridge and Kathleen Fitzpatrick

2 Flowers of Deceit Insects help angiosperms to reproduce sexually with physically distant members of their own species For example, male long-horned bees mistake Ophrys flowers for females and attempt to mate with them The flower is pollinated in the process Unusually, the flower does not produce nectar and the male receives no benefit

3 Figure 38.1

4 Figure 38.1a

5 Many angiosperms lure insects with nectar; both plant and pollinator benefit Mutualistic symbioses are common between plants and other species Angiosperms can reproduce sexually and asexually Angiosperms are the most important group of plants in terrestrial ecosystems and in agriculture

6 Concept 38.1: Flowers, double fertilization, and fruits are key features of the angiosperm life cycle Plant life cycles are characterized by the alternation between sporophyte (spore-producing) and gametophyte (gamete-producing) generations

7 In angiosperms, the sporophyte is the plant that we see; they are larger, more conspicuous and longer-lived than gametophytes The angiosperm life cycle is characterized by three Fs : flowers, double fertilization, and fruits

8 Flower Structure and Function Flowers are the reproductive shoots of the angiosperm sporophyte; they attach to a part of the stem called the receptacle Flowers consist of four floral organs: carpels, stamens, petals, and sepals Stamens and carpels are reproductive organs; sepals and petals are sterile

9 Figure 38.2 Stamen Anther Filament Stigma Carpel Style Ovary Petal Sepal Receptacle Ovule

10 Video: Flower Blooming (Time Lapse)

11 A 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 A single carpel or group of fused carpels is called a pistil A stamen consists of a filament topped by an anther with pollen sacs that produce pollen

12 Complete flowers contain all four floral organs Incomplete flowers lack one or more floral organs, for example stamens or carpels Clusters of flowers are called inflorescences

13 Much of floral diversity represents adaptation to specific pollinators Four general trends can be seen in the evolution of flowers Bilateral symmetry Reduction in the number of floral parts Fusion of floral parts Location of ovaries inside receptacles

14 Figure 38.3a Bilateral symmetry Musk mallow (radial symmetry) Bramley orchid (bilateral symmetry)

15 Figure 38.3aa Musk mallow (radial symmetry)

16 Figure 38.3ab Bramley orchid (bilateral symmetry)

17 Figure 38.3b Reduction in number of floral parts Bloodroot Drooping trillium

18 Figure 38.3ba Bloodroot

19 Figure 38.3bb Drooping trillium

20 Figure 38.3c Fusion of floral parts Star of Bethlehem Hedge bindweed

21 Figure 38.3ca Star of Bethlehem

22 Figure 38.3cb Hedge bindweed

23 Figure 38.3d Ovaries located inside receptacles Ovary Stone plant (longitudinal section) Ovary Japanese quince (longitudinal section)

24 Figure 38.3da Stone plant (longitudinal section) Ovary

25 Figure 38.3db Ovary Japanese quince (longitudinal section)

26 The Angiosperm Life Cycle: An Overview The angiosperm life cycle includes Gametophyte development Pollination Double fertilization Seed development

27 Figure Carpel Mature flower on sporophyte plant (2n) Anther Microsporangium (pollen sac) Microsporocytes (2n) MEIOSIS Male gametophyte (in pollen grain) (n) Microspore (n) Generative cell Tube cell Tube nucleus Pollen grains Key Haploid (n) Diploid (2n)

28 Figure Carpel Mature flower on sporophyte plant (2n) Anther Ovary Ovule with megasporangium (2n) MEIOSIS Microsporangium (pollen sac) Microsporocytes (2n) MEIOSIS Male gametophyte (in pollen grain) (n) Microspore (n) Generative cell Tube cell Tube nucleus Pollen grains Female gametophyte (embryo sac) Antipodal cells Polar nuclei in central cell Synergids Egg (n) Megasporangium (2n) Surviving megaspore (n) Integuments Micropyle Key Haploid (n) Diploid (2n)

29 Figure Carpel Mature flower on sporophyte plant (2n) Anther Ovary Ovule with megasporangium (2n) Female gametophyte (embryo sac) Antipodal cells Polar nuclei in central cell Synergids Egg (n) MEIOSIS Microsporangium (pollen sac) Microsporocytes (2n) MEIOSIS Male gametophyte (in pollen grain) (n) Microspore (n) Megasporangium (2n) Surviving megaspore (n) Integuments Micropyle Style Generative cell Tube cell Tube nucleus Pollen grains Stigma Pollen tube Sperm Tube nucleus Egg nucleus (n) FERTILIZATION Key Haploid (n) Diploid (2n) Discharged sperm nuclei (n)

30 Figure Carpel Mature flower on sporophyte plant (2n) Germinating seed Anther Ovary Ovule with megasporangium (2n) Embryo (2n) Endosperm (3n) Seed coat (2n) Female gametophyte (embryo sac) Seed Antipodal cells Polar nuclei in central cell Synergids Egg (n) MEIOSIS Microsporangium (pollen sac) Microsporocytes (2n) MEIOSIS Male gametophyte (in pollen grain) (n) Microspore (n) Megasporangium (2n) Surviving megaspore (n) Integuments Micropyle Style Generative cell Tube cell Tube nucleus Pollen grains Stigma Pollen tube Sperm Tube nucleus Nucleus of developing endosperm (3n) Zygote (2n) Egg nucleus (n) FERTILIZATION Key Haploid (n) Diploid (2n) Discharged sperm nuclei (n)

31 Figure 38.4a Carpel Anther Microsporangium (pollen sac) Microsporocytes (2n) Key Haploid (n) Diploid (2n) MEIOSIS Male gametophyte (in pollen grain) (n) Microspore (n) Generative cell Tube cell Tube nucleus

32 Figure 38.4b Ovary Ovule with megasporangium (2n) MEIOSIS Key Haploid (n) Diploid (2n) Megasporangium (2n) Surviving megaspore (n) Integuments Micropyle

33 Figure 38.4c Female gametophyte (embryo sac) Antipodal cells Polar nuclei in central cell Synergids Egg (n) Megasporangium (2n) Surviving megaspore (n) Integuments Micropyle Style Pollen grains Stigma Pollen tube Sperm Tube nucleus Key Haploid (n) Diploid (2n)

34 Figure 38.4d Embryo (2n) Endosperm (3n) Seed coat (2n) Seed Female gametophyte (embryo sac) Antipodal cells Polar nuclei in central cell Synergids Egg (n) Style Nucleus of developing endosperm (3n) Zygote (2n) FERTILIZATION Egg nucleus (n) Key Haploid (n) Diploid (2n) Discharged sperm nuclei (n)

35 Video: Flowering Plant Life Cycle (Time Lapse)

36 Animation: Plant Fertilization

37 Gametophyte Development Angiosperm gametophytes are microscopic and their development is obscured by protective tissues

38 Development of Female Gametophytes (Embryo Sacs) The embryo sac, or female gametophyte, develops within the ovule Within an ovule, two integuments surround a megasporangium One cell in the megasporangium undergoes meiosis, producing four megaspores, only one of which survives

39 The megaspore divides without cytokinesis, producing one large cell with eight nuclei This cell is partitioned into a multicellular female gametophyte, the embryo sac

40 Development of Male Gametophytes in Pollen Grains Pollen develops from microspores within the microsporangia, or pollen sacs, of anthers Each microspore undergoes mitosis to produce two cells: the generative cell and the tube cell A pollen grain consists of the two-celled male gametophyte and the spore wall

41 Pollination In angiosperms, pollination is the transfer of pollen from an anther to a stigma After landing on a receptive stigma, a pollen grain produces a pollen tube that grows down into the ovary and discharges two sperm cells near the embryo sac

42 Double Fertilization Fertilization, the fusion of gametes, occurs after the two sperm reach the female gametophyte One sperm fertilizes the egg, and the other combines with the two polar nuclei, giving rise to the triploid food-storing endosperm (3n) This double fertilization ensures that endosperm only develops in ovules containing fertilized eggs

43 Seed Development After double fertilization, each ovule develops into a seed The ovary develops into a fruit enclosing the seed When a seed germinates, the embryo develops into a new sporophyte

44 Methods of Pollination The transfer of pollen from anthers to stigma can be accomplished by wind, water, or animals Wind-pollinated species (e.g., grasses and many trees) release large amounts of pollen

45 Figure 38.5a Abiotic pollination by wind Pollination by bees Hazel carpellate flower (carpels only) Hazel staminate flowers (stamens only) releasing clouds of pollen Common dandelion under normal light Common dandelion under ultraviolet light

46 Figure 38.5aa Hazel carpellate flower (carpels only)

47 Figure 38.5ab Hazel staminate flowers (stamens only) releasing clouds of pollen

48 Figure 38.5ac Common dandelion under normal light

49 Figure 38.5ad Common dandelion under ultraviolet light

50 Figure 38.5b Pollination by moths and butterflies Pollination by bats Pollination by flies Anther Moth Stigma Moth on yucca flower Pollination by birds Long-nosed bat feeding on cactus flower at night Blowfly on carrion flower Hummingbird drinking nectar of columbine flower

51 Figure 38.5ba Anther Moth Stigma Moth on yucca flower

52 Figure 38.5bb Long-nosed bat feeding on cactus flower at night

53 Figure 38.5bc Blowfly on carrion flower

54 Figure 38.5bd Hummingbird drinking nectar of columbine flower

55 Video: Bat Pollinating Agave Plant

56 Video: Bee Pollinating

57 Coevolution is the joint evolution of interacting species in response to selection imposed by each other Many flowering plants have coevolved with specific pollinators The shapes and sizes of flowers often correspond to the pollen transporting parts of their animal pollinators For example, Darwin correctly predicted a moth with a 28-cm-long tongue based on the morphology of a particular flower

58 Figure 38.6

59 From Seed to Flowering Plant: A Closer Look The development of a seed into a flowering plant includes several stages Endosperm development Embryo development Seed dormancy Seed germination Seedling development Flowering

60 Endosperm Development Endosperm development usually precedes embryo development In most monocots and many eudicots, endosperm stores nutrients that can be used by the seedling In other eudicots, the food reserves of the endosperm are exported to the cotyledons

61 Embryo Development The first mitotic division of the zygote splits the fertilized egg into a basal cell and a terminal cell The basal cell produces a multicellular suspensor, which anchors the embryo to the parent plant The terminal cell gives rise to most of the embryo The cotyledons form and the embryo elongates

62 Figure 38.7 Ovule Endosperm nucleus Zygote Integuments Zygote Terminal cell Basal cell Proembryo Suspensor Basal cell Cotyledons Shoot apex Root apex Suspensor Seed coat Endosperm

63 Animation: Seed Development

64 Structure of the Mature Seed The embryo and its food supply are enclosed by a hard, protective seed coat The seed enters a state of dormancy A mature seed is only about 5 15% water

65 In some eudicots, such as the common garden bean, the embryo consists of the embryonic axis attached to two fleshy cotyledons (seed leaves) Below the cotyledons the embryonic axis is called the hypocotyl and terminates in the radicle (embryonic root); above the cotyledons it is called the epicotyl The plumule comprises the epicotyl, young leaves, and shoot apical meristem

66 Figure 38.8 Seed coat Epicotyl Hypocotyl Radicle Cotyledons (a) Common garden bean, a eudicot with thick cotyledons Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle (b) Castor bean, a eudicot with thin cotyledons (c) Maize, a monocot Scutellum (cotyledon) Coleoptile Coleorhiza Pericarp fused with seed coat Endosperm Epicotyl Hypocotyl Radicle

67 Figure 38.8a Seed coat Radicle Epicotyl Hypocotyl Cotyledons (a) Common garden bean, a eudicot with thick cotyledons

68 Figure 38.8b Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle (b) Castor bean, a eudicot with thin cotyledons

69 Figure 38.8c (c) Maize, a monocot Scutellum (cotyledon) Coleoptile Coleorhiza Pericarp fused with seed coat Endosperm Epicotyl Hypocotyl Radicle

70 The seeds of some eudicots, such as castor beans, have thin cotyledons

71 A monocot embryo has one cotyledon Grasses, such as maize and wheat, have a special cotyledon called a scutellum Two sheathes enclose the embryo of a grass seed: a coleoptile covering the young shoot and a coleorhiza covering the young root

72 Seed Dormancy: An Adaptation for Tough Times 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 Most seeds remain viable after a year or two of dormancy, but some last only days and others can remain viable for centuries

73 Seed Germination and Seedling Development Germination depends on imbibition, the uptake of water due to low water potential of the dry seed The radicle (embryonic root) emerges first; the developing root system anchors the plant Next, the shoot tip breaks through the soil surface

74 In many eudicots, a hook forms in the hypocotyl, and growth pushes the hook above ground Light causes the hook to straighten and pull the cotyledons and shoot tip up

75 Figure 38.9 Foliage leaves Cotyledon Hypocotyl Cotyledon Hypocotyl Epicotyl Cotyledon Hypocotyl Radicle Seed coat (a) Common garden bean Foliage leaves Coleoptile Coleoptile (b) Maize Radicle

76 Figure 38.9a Foliage leaves Cotyledon Hypocotyl Cotyledon Hypocotyl Epicotyl Cotyledon Hypocotyl Radicle Seed coat (a) Common garden bean

77 Figure 38.9b Foliage leaves Coleoptile Coleoptile (b) Maize Radicle

78 In maize and other grasses, which are monocots, the coleoptile pushes up through the soil creating a tunnel for the shoot tip to grow through

79 Flowering The flowers of a given plant species are synchronized to appear at a specific time of the year to promote outbreeding Flowering is triggered by a combination of environmental cues and internal signals

80 Fruit Structure and Function A fruit is the mature ovary of a flower It protects the enclosed seeds and aids in seed dispersal by wind or animals In some fruits, such as soybean pods, the ovary wall dries out at maturity, whereas in other fruits, such as grapes, it remains fleshy

81 Figure 38.10

82 Fruits are classified based on their developmental origin Simple fruits develop from a single or several fused carpels Aggregate fruits result from a single flower with multiple separate carpels Multiple fruits develop from a group of flowers called an inflorescence

83 Figure Stamen Ovary Carpels Stamen Flowers Stigma Petal Style Pea flower Seed Stigma Ovule Carpel (fruitlet) Raspberry flower Stigma Ovary Pineapple inflorescence Each segment develops from the carpel of one flower Sepal Ovule Stamen Ovary (in receptacle) Apple flower Remains of stamens and styles Sepals Pea fruit Raspberry fruit Stamen Pineapple fruit Seed Receptacle Apple fruit (a) Simple fruit (b) Aggregate fruit (c) Multiple fruit (d) Accessory fruit

84 Figure 38.11a Stamen Ovary Carpels Stamen Pea flower Stigma Ovule Raspberry flower Seed Carpel (fruitlet) Stigma Ovary Stamen Pea fruit (a) Simple fruit Raspberry fruit (b) Aggregate fruit

85 Figure 38.11b Flowers Petal Stigma Style Pineapple inflorescence Each segment develops from the carpel of one flower Sepal Ovule Apple flower Stamen Ovary (in receptacle) Remains of stamens and styles Sepals Pineapple fruit (c) Multiple fruit Seed Receptacle Apple fruit (d) Accessory fruit

86 Animation: Fruit Development

87 An accessory fruit contains other floral parts in addition to ovaries

88 Fruit dispersal mechanisms include Water Wind Animals

89 Figure 38.12a Dispersal by water Dispersal by wind Coconut seed embryo, endosperm, and endocarp inside buoyant husk Giant seed of the tropical Asian climbing gourd Alsomitra macrocarpa Dandelion fruit Dandelion seeds (actually one-seeded fruits) Winged fruit of a maple Tumbleweed

90 Figure 38.12aa Coconut seed embryo, endosperm, and endocarp inside buoyant husk

91 Figure 38.12ab Giant seed of the tropical Asian climbing gourd Alsomitra macrocarpa

92 Figure 38.12ac Dandelion fruit Dandelion seeds (actually one-seeded fruits)

93 Figure 38.12ad Winged fruit of a maple

94 Figure 38.12ae Tumbleweed

95 Figure 38.12b Dispersal by animals Fruit of puncture vine (Tribulus terrestris) Squirrel hoarding seeds or fruits underground Ant carrying seed with attached food body Seeds dispersed in black bear feces

96 Figure 38.12ba Fruit of puncture vine (Tribulus terrestris)

97 Figure 38.12bb Squirrel hoarding seeds or fruits underground

98 Figure 38.12bc Seeds dispersed in black bear feces

99 Figure 38.12bd Ant carrying seed with attached food body

100 Concept 38.2: Flowering plants reproduce sexually, asexually, or both Many angiosperm species reproduce both asexually and sexually Sexual reproduction results in offspring that are genetically different from their parents Asexual reproduction results in a clone of genetically identical organisms

101 Mechanisms of Asexual Reproduction Fragmentation, separation of a parent plant into parts that develop into whole plants, is a very common type of asexual reproduction In some species, a parent plant s root system gives rise to adventitious shoots that become separate shoot systems

102 Figure 38.13

103 Apomixis is the asexual production of seeds from a diploid cell

104 Advantages and Disadvantages of Asexual and Sexual Reproduction Asexual reproduction is also called vegetative reproduction because progeny arise from mature vegetative fragments All genetic material is passed to the progeny Asexual reproduction can be beneficial to a successful plant in a stable environment However, a clone of plants is vulnerable to local extinction if there is an environmental change

105 Sexual reproduction generates genetic variation that makes evolutionary adaptation possible However, only a fraction of seedlings survive Some flowers can self-fertilize to ensure that every ovule will develop into a seed However, many species have evolved mechanisms to prevent selfing

106 Mechanisms That Prevent Self-Fertilization Many angiosperms have mechanisms that make it difficult or impossible for a flower to self-fertilize Dioecious species have staminate and carpellate flowers on separate plants

107 Figure (a) Staminate flowers (left) and carpellate flowers (right) of a dioecious species Stamens Styles Styles Stamens Thrum flower (b) Thrum and pin flowers Pin flower

108 Figure 38.14a Staminate flower

109 Figure 38.14b Carpellate flower

110 Figure 38.14c Stamens Styles Styles Stamens Thrum flower Pin flower

111 Others have stamens and carpels that mature at different times or are arranged to prevent selfing

112 The most common is self-incompatibility, a plant s ability to reject its own pollen Researchers are unraveling the molecular mechanisms involved in self-incompatibility Some plants reject pollen that has an S-gene matching an allele in the stigma cells Recognition of self pollen triggers a signal transduction pathway leading to a block in growth of a pollen tube

113 Totipotency, Vegetative Reproduction, and Tissue Culture Totipotent cells, those that can divide and asexually generate a clone of the original organism, are common in plants Humans have devised methods for asexual propagation of angiosperms Most methods are based on the ability of plants to form adventitious roots or shoots

114 Vegetative Propagation and Grafting Vegetative reproduction that is facilitated or induced by humans is called vegetative propagation Many kinds of plants are asexually reproduced from plant fragments called cuttings A callus is a mass of dividing, undifferentiated totipotent cells that forms where a stem is cut and produces adventitious roots

115 A twig or bud can be grafted onto a plant of a closely related species or variety The stock provides the root system The scion is grafted onto the stock

116 Test-Tube Cloning and Related Techniques Plant biologists have adopted in vitro methods to create and clone novel plant varieties A callus of undifferentiated totipotent cells can sprout shoots and roots in response to plant hormones

117 Figure (a) (b) (c) Developing root

118 Some pathogenic viruses can be eliminated by excising virus-free apical meristems for tissue culture Plant tissue culture also facilitates the production of genetically modified (GM) plants

119 Concept 38.3: People modify crops by breeding and genetic engineering People have intervened in the reproduction and genetic makeup of plants for thousands of years Hybridization is common in nature and has been used by breeders to introduce new genes Maize, a product of artificial selection, is a staple in many developing countries

120 Figure 38.16

121 Figure 38.16a

122 Figure 38.16b

123 Plant Breeding Mutations can arise spontaneously or can be induced by breeders Plants with beneficial mutations are used in breeding experiments Desirable traits can be introduced from different species or genera

124 Plant Biotechnology and Genetic Engineering Plant biotechnology has two meanings In a general sense, it refers to innovations in the use of plants to make useful products In a specific sense, it refers to use of GM organisms in agriculture and industry Transgenic organisms are those that have been engineered to express a gene from another species

125 Reducing World Hunger and Malnutrition Genetically modified plants may increase the quality and quantity of food worldwide Some transgenic crops have been developed to produce the Bt toxin, which is toxic to insect pests Other crops are able to tolerate herbicides or resist specific diseases

126 Figure Non-Bt maize Bt maize

127 Nutritional quality of plants is being improved For example, Golden Rice is a transgenic variety being developed to address vitamin A deficiencies among the world s poor For example, transgenic cassava have increased levels of iron and beta-carotene and reduced cyanide-producing chemicals

128 Figure 38.18

129 Reducing Fossil Fuel Dependency Biofuels are fuels derived from living biomass, the total mass of organic matter in a group of organisms Biofuels can be produced by rapidly growing crops such as switchgrass and poplar Biofuels would reduce the net emission of CO 2, a greenhouse gas

130 The Debate over Plant Biotechnology Some biologists are concerned about risks of releasing GM organisms (GMOs) into the environment

131 Issues of Human Health One concern is that genetic engineering may transfer allergens from a gene source to a plant used for food Some GMOs have health benefits For example, maize that produces the Bt toxin has 90% less of a cancer-causing toxin than non-bt corn Bt maize has less insect damage and lower infection by Fusarium fungus that produces the cancer-causing toxin

132 Widespread adoption of Bt cotton in India has led to a 41% decrease in insecticide use and an 80% reduction in acute poisoning cases

133 Possible Effects on Nontarget Organisms Many ecologists are concerned that the growing of GM crops might have unforeseen effects on nontarget organisms

134 Addressing the Problem of Transgene Escape Perhaps the most serious concern is the possibility of introduced genes escaping into related weeds through crop-to-weed hybridization This could result in superweeds that would be resistant to many herbicides

135 Efforts are underway to prevent this by introducing Male sterility Apomixis Transgenes into chloroplast DNA (not transferred by pollen) Strict self-pollination

136 Figure 38.UN01a

137 Figure 38.UN01aa

138 Figure 38.UN01ab

139 Figure 38.UN01b

140 Figure 38.UN02 Tube nucleus One sperm will fuse with the egg, forming a zygote (2n). One sperm cell will fuse with the 2 polar nuclei, forming an endosperm nucleus (3n).

141 Figure 38.UN03

2014 Pearson Education, Inc. 1

2014 Pearson Education, Inc. 1 1 Stamen Anther Filament Stigma Carpel Style Ovary Petal Sepal Ovule 2 A B Sepals Petals Stamens Carpels C A + B gene activity B + C gene activity C gene activity Carpel Petal (a) A schematic diagram of