Angiosperm Reproduction and Biotechnology

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Campsoscolia wasps 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

1 LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson Chapter 38 Angiosperm Reproduction and Biotechnology Overview: Flowers of Deceit Insects help angiosperms to reproduce sexually with distant members of their own species For example, male Campsoscolia wasps 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 Lectures by Erin Barley Kathleen Fitzpatrick Copyright 2011 Pearson 2008 Education, Pearson Education, Inc. Inc., publishing as Pearson Benjamin Cummings Figure 38.1 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 Copyright 2011 Pearson 2008 Education, Pearson Education, Inc. Inc., publishing as Pearson Benjamin Cummings Concept 38.1: Flowers, double fertilization, and fruits are unique features of the angiosperm life cycle Plant lifecycles are characterized by the alternation between a multicellular haploid (n) generation and a multicellular diploid (2n) generation Diploid sporophytes (2n) produce spores (n) by meiosis; these grow into haploid gametophytes (n) Gametophytes produce haploid gametes (n) by mitosis; fertilization of gametes produces a sporophyte Video: Flower Blooming (time lapse) In angiosperms, the sporophyte is the dominant generation, the large plant that we see The gametophytes are reduced in size and depend on the sporophyte for nutrients The angiosperm life cycle is characterized by three Fs : flowers, double fertilization, and fruits Video: Flower Plant Life Cycle (time lapse) 1

Structure of an idealized flower Sepal Key Haploid (n) Diploid (2n) (b) Simplified angiosperm life cycle Mature sporophyte plant (2n) Germinating seed Seed Egg (n) Sperm (n) Seed FERTILIZATION Zygote

2b Key Haploid (n) Diploid (2n) Anther Pollen tube Mature sporophyte plant (2n) Germinating seed Seed Germinated pollen grain (n) (male gametophyte) Embryo sac (n) (female gametophyte) Egg (n) Sperm

2 Figure 38.2 Figure 38.2a Stamen Anther Filament Carpel Style Anther Pollen tube Germinated pollen grain (n) (male gametophyte) Embryo sac (n) (female gametophyte) Stamen Anther Filament Carpel Style Petal Receptacle (a) Structure of an idealized flower Sepal Key Haploid (n) Diploid (2n) (b) Simplified angiosperm life cycle Mature sporophyte plant (2n) Germinating seed Seed Egg (n) Sperm (n) Seed FERTILIZATION Zygote (2n) Simple fruit Embryo (2n) (sporophyte) Petal Sepal Receptacle (a) Structure of an idealized flower Figure 38.2b Key Haploid (n) Diploid (2n) Anther Pollen tube Mature sporophyte plant (2n) Germinating seed Seed Germinated pollen grain (n) (male gametophyte) Embryo sac (n) (female gametophyte) Egg (n) Sperm (n) Seed FERTILIZATION Zygote (2n) 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: sepals, petals, stamens, and carpels Stamens and carpels are reproductive organs; sepals and petals are sterile (b) Simplified angiosperm life cycle Simple fruit Embryo (2n) (sporophyte) A stamen consists of a filament topped by an anther with pollen sacs that produce pollen 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 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 2

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

3 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 If pollination succeeds, a pollen grain produces a pollen tube that grows down into the ovary and discharges two sperm cells near the embryo sac Video: Bee Pollinating Video: Bat Pollinating Agave Plant Figure 38.3 (a) Development of a male gametophyte (in pollen grain) Microsporangium (pollen sac) (b) Development of a female gametophyte (embryo sac) Megasporangium Figure 38.3a (a) Development of a male gametophyte (in pollen grain) Microsporangium (pollen sac) Microsporocyte Megasporocyte Microsporocyte MEIOSIS Integuments MEIOSIS Microspores (4) Micropyle Microspores (4) Each of 4 microspores Generative cell (will form 2 sperm) 75 µm (LM) 20 µm Male gametophyte (in pollen grain) Nucleus of tube cell Ragweed pollen grain (colorized SEM) MITOSIS Key to labels Haploid (n) Diploid (2n) Integuments 100 µm Surviving megaspore Antipodal cells (3) Polar nuclei (2) Egg (1) Synergids (2) Embryo sac (LM) Female gametophyte (embryo sac) Each of 4 microspores Generative cell (will form 2 sperm) 75 µm (LM) 20 µm MITOSIS Male gametophyte (in pollen grain) Nucleus of tube cell Ragweed pollen grain (colorized SEM) Key to labels Haploid (n) Diploid (2n) 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 The megaspore divides, producing a large cell with eight nuclei This cell is partitioned into a multicellular female gametophyte, the embryo sac 3

Figure 38.3b (b) Development of a female gametophyte (embryo sac) Figure 38.

cell (will form 2 sperm) Nucleus of tube cell MITOSIS Key to labels Haploid (n) Diploid (2n)

Female gametophyte (embryo sac) 75 µm (LM) Figure 38.3d Figure 38.

angiosperms, pollination is the transfer of pollen from an anther to a stigma Pollination can

, grasses and many trees) release large amounts of pollen Figure 38.

4 Figure 38.3b (b) Development of a female gametophyte (embryo sac) Figure 38.3c Megasporangium Megasporocyte MEIOSIS Integuments Micropyle Surviving megaspore Generative cell (will form 2 sperm) Nucleus of tube cell MITOSIS Key to labels Haploid (n) Diploid (2n) Integuments 100 µm Antipodal cells (3) Polar nuclei (2) Egg (1) Synergids (2) Embryo sac (LM) Female gametophyte (embryo sac) 75 µm (LM) Figure 38.3d Figure 38.3e 20 µm Ragweed pollen grain (colorized SEM) 100 µm Embryo sac (LM) Pollination In angiosperms, pollination is the transfer of pollen from an anther to a stigma Pollination can be by wind, water, or animals Wind-pollinated species (e.g., grasses and many trees) release large amounts of pollen Figure 38.4a Abiotic Pollination by Wind Hazel staminate flowers (stamens only) Hazel carpellate flower (carpels only) Pollination by Bees Common dandelion under normal light Common dandelion under ultraviolet light 4

Hazel staminate flowers (stamens only) Figure

4ad Common dandelion under ultraviolet light

4ba Pollination by Bats Anther Anther Moth

carrion flower Long-nosed bat feeding on

5 1/15/14 Figure 38.4aa Figure 38.4ab Hazel carpellate flower (carpels only) Hazel staminate flowers (stamens only) Figure 38.4ac Figure 38.4ad Common dandelion under ultraviolet light Common dandelion under normal light Figure 38.4b Pollination by Moths and Butterflies Pollination by Flies Figure 38.4ba Pollination by Bats Anther Anther Moth Fly egg Moth Moth on yucca flower Blowfly on carrion flower Long-nosed bat feeding on cactus flower at night Pollination by Birds Hummingbird drinking nectar of columbine flower Moth on yucca flower 5

Figure 38.4bb Figure 38.4bc Fly egg Blowfly on carrion flower Long-nosed bat feeding on cactus flower at night Figure 38.

interacting species in response to changes in each other Many flowering plants have coevolved with specific pollinators The

correctly predicted a moth with a 28 cm long tongue based on the morphology of a particular flower Figure 38.

of the style toward the ovary Double fertilization results from the discharge of two sperm from the pollen tube into the embryo

6 Figure 38.4bb Figure 38.4bc Fly egg Blowfly on carrion flower Long-nosed bat feeding on cactus flower at night Figure 38.4bd Hummingbird drinking nectar of columbine flower Coevolution of Flower and Pollinator Coevolution is the evolution of interacting species in response to changes in 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 Figure 38.5 Double Fertilization After landing on a receptive stigma, a pollen grain produces a pollen tube that extends between the cells of the style toward the ovary Double fertilization results from the discharge of two sperm from the pollen tube into the embryo sac One sperm fertilizes the egg, and the other combines with the polar nuclei, giving rise to the triploid food-storing endosperm (3n) Animation: Plant Fertilization 6

7 Figure Figure Pollen tube 2 sperm Style Pollen grain 1 Pollen tube 2 sperm Style Pollen grain 2 Polar nuclei Egg Polar nuclei Polar nuclei Synergid 2 sperm Micropyle Egg Micropyle Egg Figure Seed Development, Form, and Function 1 Pollen tube 2 sperm Style Micropyle Pollen grain Polar nuclei Egg 2 3 Endosperm nucleus (3n) (2 polar nuclei plus sperm) Polar nuclei Egg Synergid 2 sperm Zygote (2n) 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 In most monocots and some 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 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 Animation: Seed Development 7

Zygote Zygote Terminal cell Basal cell Figure 38.

8 Figure 38.7 Figure 38.7a Zygote Proembryo Endosperm nucleus Suspensor Integuments Cotyledons Zygote Terminal cell Basal cell Basal cell Shoot apex Root apex Suspensor Seed coat Endosperm Endosperm nucleus Integuments Zygote Zygote Terminal cell Basal cell Figure 38.7b Proembryo Suspensor Basal cell Cotyledons Shoot apex Root apex Suspensor Seed coat 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 Endosperm Figure 38.8 Seed coat Epicotyl In some eudicots, such as the common garden bean, the embryo consists of the embryonic axis attached to two thick 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 Radicle Cotyledons (a) Common garden bean, a eudicot with thick cotyledons (b) Castor bean, a eudicot with thin cotyledons (c) Maize, a monocot Scutellum (cotyledon) Coleoptile Coleorhiza Seed coat Endosperm Cotyledons Epicotyl Radicle Pericarp fused with seed coat Endosperm Epicotyl Radicle 8

thick cotyledons 8b Seed coat Endosperm Cotyledons Epicotyl Radicle A monocot embryo has one cotyledon Grasses, such as maize and wheat, have a special

root (b) Castor bean, a eudicot with thin cotyledons 8c (c) Maize, a monocot Scutellum (cotyledon) Coleoptile Coleorhiza Pericarp fused with seed coat

9 Figure 38.8a Seed coat Radicle Epicotyl Cotyledons The seeds of some eudicots, such as castor beans, have thin cotyledons (a) Common garden bean, a eudicot with thick cotyledons Figure 38.8b Seed coat Endosperm Cotyledons Epicotyl Radicle 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 (b) Castor bean, a eudicot with thin cotyledons Figure 38.8c (c) Maize, a monocot Scutellum (cotyledon) Coleoptile Coleorhiza Pericarp fused with seed coat Endosperm Epicotyl Radicle 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 9

Seed Germination and Seedling Development Germination depends on imbibition, the uptake of water due to low water potential of the dry

hypocotyl, and growth pushes the hook above ground Light causes the hook to straighten and pull the cotyledons and shoot tip up Figure 38.

9a Foliage leaves Cotyledon Epicotyl Radicle Seed coat (a) Common garden bean Foliage leaves Cotyledon Cotyledon (b) Maize Coleoptile

10 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 Next, the shoot tip breaks through the soil surface 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 Figure 38.9 Cotyledon Foliage leaves Cotyledon Epicotyl Cotyledon Figure 38.9a Foliage leaves Cotyledon Epicotyl Radicle Seed coat (a) Common garden bean Foliage leaves Cotyledon Cotyledon (b) Maize Coleoptile Coleoptile Radicle Radicle Seed coat (a) Common garden bean Figure 38.9b In maize and other grasses, which are monocots, the coleoptile pushes up through the soil Coleoptile Coleoptile Foliage leaves (b) Maize Radicle 10

Fruit Form and Function A fruit develops from the ovary It protects the enclosed seeds and aids in seed dispersal by wind or animals A fruit may be classified as dry, if the ovary dries out at

11 Fruit Form and Function A fruit develops from the ovary It protects the enclosed seeds and aids in seed dispersal by wind or animals A fruit may be classified as dry, if the ovary dries out at maturity, or fleshy, if the ovary becomes thick, soft, and sweet at maturity Fruits are also classified by their development Simple, a single or several fused carpels Aggregate, a single flower with multiple separate carpels Multiple, a group of flowers called an inflorescence Animation: Fruit Development Figure Figure 38.10a Stamen Carpels Stamen Flower Petal Style Stamen Carpels Stamen Pea flower Seed Pea fruit Raspberry flower Carpel (fruitlet) Raspberry fruit Stamen Pineapple inflorescence Each segment develops from the carpel of one flower Pineapple fruit Stamen Sepal (in receptacle) Apple flower Remains of stamens and styles Sepals Seed Receptacle Apple fruit (a) Simple fruit (b) Aggregate fruit (c) Multiple fruit (d) Accessory fruit Pea flower Seed Pea fruit (a) Simple fruit Raspberry flower Carpel (fruitlet) Raspberry fruit (b) Aggregate fruit Stamen Figure 38.10b Flower Petal Style Pineapple inflorescence Each segment develops from the carpel of one flower Pineapple fruit (c) Multiple fruit Stamen Sepal (in receptacle) Apple flower Remains of stamens and styles Sepals Seed Receptacle Apple fruit (d) Accessory fruit An accessory fruit contains other floral parts in addition to ovaries 11

Water Wind Animals Dandelion seeds (actually one-seeded

Dispersal by Water Winged seed of the tropical Asian climbing

and endocarp inside buoyant husk 11aa 11ab Coconut seed

seed of the tropical Asian climbing gourd Alsomitra

12 Figure 38.11a Dispersal by Wind Fruit dispersal mechanisms include Water Wind Animals Dandelion seeds (actually one-seeded fruits) Winged fruit of a maple Dandelion fruit Tumbleweed Dispersal by Water Winged seed of the tropical Asian climbing gourd Alsomitra macrocarpa Coconut seed embryo, endosperm, and endocarp inside buoyant husk Figure 38.11aa Figure 38.11ab Coconut seed embryo, endosperm, and endocarp inside buoyant husk Winged seed of the tropical Asian climbing gourd Alsomitra macrocarpa Figure 38.11ac Figure 38.11ad Dandelion fruit Dandelion seeds (actually one-seeded fruits) Winged fruit of a maple 12

Tumbleweed Seeds dispersed in black bear

13 1/15/14 Figure 38.11ae Figure 38.11b Dispersal by Animals Fruit of puncture vine (Tribulus terrestris) Squirrel hoarding seeds or fruits underground Ant carrying seed with nutritious food body to its nest Tumbleweed Seeds dispersed in black bear feces Figure 38.11ba Figure 38.11bb Fruit of puncture vine (Tribulus terrestris) Figure 38.11bc Squirrel hoarding seeds or fruits underground Figure 38.11bd Ant carrying seed with nutritious food body to its nest Seeds dispersed in black bear feces 13

14 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 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 Figure Apomixis is the asexual production of seeds from a diploid cell Advantages and Disadvantages of Asexual Versus Sexual Reproduction Asexual reproduction is also called vegetative reproduction 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 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 Many species have evolved mechanisms to prevent selfing 14

that make it difficult or impossible for a flower to self-fertilize Dioecious

flowers (left) and carpellate flowers (right) of a dioecious species Stamens

13b Staminate flowers Carpellate flowers 13c Others have stamens and carpels

15 Figure 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 (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 Figure 38.13a Figure 38.13b Staminate flowers Carpellate flowers Figure 38.13c Others have stamens and carpels that mature at different times or are arranged to prevent selfing Stamens Styles Styles Stamens Thrum flower Pin flower 15

Vegetative Propagation and Agriculture The most common is self-incompatibility, a plant s ability to reject its own pollen Researchers are unraveling the molecular mechanisms involved in

16 Vegetative Propagation and Agriculture 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 Humans have devised methods for asexual propagation of angiosperms Most methods are based on the ability of plants to form adventitious roots or shoots Clones from Cuttings Many kinds of plants are asexually reproduced from plant fragments called cuttings A callus is a mass of dividing undifferentiated cells that forms where 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 The stock provides the root system The scion is grafted onto the stock Copyright 2011 Pearson 2008 Education, Pearson Education, Inc. Inc., publishing as Pearson Benjamin Cummings Test-Tube Cloning and Related Techniques Figure Plant biologists have adopted in vitro methods to create and clone novel plant varieties A callus of undifferentiated cells can sprout shoots and roots in response to plant hormones (a) (b) (c) Developing root 16

another organism Protoplast fusion is used to create hybrid plants by

intervened in the reproduction and genetic makeup of plants for thousands

17 Figure Transgenic plants are genetically modified (GM) to express a gene from another organism Protoplast fusion is used to create hybrid plants by fusing protoplasts, plant cells with their cell walls removed 50 µm Concept 38.3: Humans modify crops by breeding and genetic engineering Figure Humans 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 Figure 38.16a Figure 38.16b 17

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

18 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 The grain triticale is derived from a successful cross between wheat and rye 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 Modern plant biotechnology is not limited to transfer of genes between closely related species or varieties of the same species 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 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 Figure Reducing Fossil Fuel Dependency Biofuels are made by the fermentation and distillation of plant materials such as cellulose 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 The environmental implications of biofuels are controversial Cassava roots harvested in Thailand 18

19 The Debate over Plant Biotechnology Some biologists are concerned about risks of releasing GM organisms (GMOs) into the environment 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 Possible Effects on Nontarget Organisms GMO opponents advocate for clear labeling of all GMO foods Many ecologists are concerned that the growing of GM crops might have unforeseen effects on nontarget organisms 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 Efforts are underway to prevent this by introducing Male sterility Apomixis Transgenes into chloroplast DNA (not transferred by pollen) Strict self-pollination 19

20 Figure 38.UN01 Figure 38.UN02 Endosperm nucleus (3n) (2 polar nuclei plus sperm) Zygote (2n) (egg plus sperm) 20

Chapter 38 Angiosperm Reproduction and Biotechnology

Chapter 38 Angiosperm Reproduction and Biotechnology Concept 38.1 Pollination enables gametes to come together within a flower Diploid (2n) sporophytes produce spores by meiosis; these grow into haploid