Angiosperm Reproduction and Biotechnology (被子植物生殖與生物技術)

1. (5) Chapter 38 Angiosperm Reproduction and Biotechnology 被子植物生殖與生物技術

2. Figure 38.1 To Be or Not to Be (??????) • Overview: To Seed or Not to Seed • The parasitic plantRafflesia arnoldii • Produces enormous flowers that can produce up to 4 million seeds

3. Key Concepts Concept 38.1: Pollination enables gametes to come together within a flower (受粉作用使得花中的配子聚在一起) Concept 38.2: After fertilization, ovules develop into seeds and ovaries into fruits Concept 38.3: Many flowering plantsclone (複製) themselves by asexual reproduction Concept 38.4: Plant biotechnology is transforming agriculture

4. Concept 38.1: Pollination enables gametes to come together within a flower (受粉作用使得花中的配子聚在一起) • In angiosperms, the dominant sporophyte (孢子體) • Produces spores that develop within flowers into male gametophytes (pollen grains) (雄配子體、花粉粒) • Produces female gametophytes (embryo sacs) (雌配子體、胚囊)

5. Flower Structure • Flowers • Are the reproductive shoots of the angiosperm sporophyte (被子植物配子體) • Are composed of four floral organs: • Sepals (萼片) • Petals (花瓣) • Stamens (雄蕊) • Carpels (雌蕊) 柱頭 花藥 Carpel雌蕊 Stigma 雄蕊Stamen Anther Style 花柱 Ovary Filament 卵房 花絲 Sepal萼片 花瓣Petal Receptacle 花托

6. 被子植物花的多樣性 • Many variations in floral structurehave evolved during the 140 million years of angiosperm history SYMMETRY OVARY LOCATION FLORAL DISTRIBUTION Bilateral symmetry (orchid) Lupine inflorescence Superior ovary Sepal Semi-inferior ovary Inferior ovary Radial symmetry (daffodil) Sunflower inflorescence Fused petals REPRODUCTIVE VARIATIONS Dioecious Sagittaria latifolia (common arrowhead) Maize, a monoecious species Figure 38.3

7. Gametophyte Development and Pollination • In angiosperms (被子植物) • Pollination(受粉作用) is the transfer of pollen from an anther(花藥) to a stigma(柱頭) • If pollination is successful, a pollen grain(花粉粒) produces a structure called a pollen tube(花粉管), which grows down into the ovary (卵房) and discharges sperm near the embryo sac (胚囊)

8. An overview of angiosperm reproduction Germinated pollen grain (n) (male gametophyte) on stigma of carpel Carpel Stigma Anther at tip of stamen Anther Stamen Style Ovary Filament Ovary (base of carpel) Pollen tube Ovule (卵胞) Embryo sac (n) (female gametophyte) Sepal Egg (n) FERTILIZATION Petal Receptacle Sperm (n) Zygote (2n) (a) An idealized flower. Mature sporophyte plant (2n) with flowers Seed (develops from ovule) Key Seed Haploid (n) Diploid (2n) (b) Simplified angiosperm life cycle.See Figure 30.10 for a more detailedversion of the life cycle, including meiosis. Embryo (2n) (sporophyte) Germinating seed Simple fruit (develops from ovary) Figure 38.2a, b

9. Development of a male gametophyte (pollen grain)雄配子體(花粉粒)的發育 (a) • Pollen (花粉)---Develops from microspores (雄孢子) within the sporangia (孢子囊) of anthers Pollen sac (microsporangium) (1) Each one of the microsporangia contains diploid microsporocytes (2n) (microspore mother cells). Micro- Sporocyte MEIOSIS減數分裂 (2) Each microsporocyte divides by meiosis to produce four haploid microspores (n), each of which develops into a pollen grain. Micro- spores (4) Each of 4 microspores MITOSIS有絲分裂 Generative cell (will form 2 sperm) Male Gametophyte (pollen grain) (3) A pollen grain becomes a mature male gametophyte when its generative nucleus divides and forms two sperm. This usually occurs after a pollen grain lands on the stigma of a carpel and the pollen tube begins to grow. (See Figure 38.2b.) Nucleus of tube cell KEY to labels 20 m Haploid (2n) Diploid (2n) 75 m Ragweedpollen grain Figure 38.4a

10. Development of a female gametophyte (embryo sac)雌配子體(胚囊)的發育 (b) • Embryo sacs---Develop from megaspores within ovules (1) Within the ovule’s megasporangium is a large diploid cell called the megasporocyte (megaspore mother cell). Mega- sporangium Ovule Mega- sporocyte 減數分裂MEIOSIS Integuments Micropyle (2) The megasporocyte divides by meiosis and gives rise to four haploid cells, but in most species only one of these survives as the megaspore. Surviving megaspore Female gametophyte (embryo sac) 有絲分裂MITOSIS Antipodel Cells (3) Ovule Polar Nuclei (2) Egg (1) (3) Three mitotic divisions of the megaspore form the embryo sac, a multicellular female gametophyte. The ovule now consists of the embryo sac along with the surrounding integuments (protective tissue). Integuments Synergids (2) Key to labels Embryo sac Haploid (2n) 100 m Diploid (2n) Figure 38.4b

11. Mechanisms That Prevent Self-Fertilization (自我受精) • Many angiosperms (被子植物) • Have mechanisms that make it difficult or impossible for a flower to fertilize itself (自我受精) Stigma 柱頭 Stigma 柱頭 Anther with Pollen 有花粉的花藥 Thrum flower Pin flower Figure 38.5

12. The most common anti-selfing mechanism in flowering plants • Is known as self-incompatibility (自我排斥、自我不相容),the ability of a plant to reject its own pollen • Researchers are unraveling the molecular mechanisms that are involved in self-incompatibility • Some plants • Reject pollen that has an S-gene matching an allele in the stigma cells • Recognition of self pollen (自家花粉) • Triggers a signal transduction pathway leading to a block (阻礙) in growth of a pollen tube

13. Concept 38.2: After fertilization, ovules develop into seeds and ovaries into fruits

14. Double Fertilization (雙重受精) • After landing on a receptive stigma (花柱) • A pollen grain(花粉粒) germinates and produces a pollen tube(花粉管) that extends down between the cells of the style () toward the ovary () • The pollen tube(花粉管) • Then discharges two sperm into the embryo sac • In double fertilization(雙重受精) • One sperm fertilizes the egg • The other sperm combines with the polar nuclei (極核), giving rise to the food-storing endosperm (胚乳)

15. Growth of the pollen tube and double fertilization (花粉粒)Pollen grain Stigma (柱頭) Pollen tube (花粉管) (1) If a pollen grain germinates, a pollen tube grows down the style toward the ovary. 2 sperm Style Ovary (極核)Polar nuclei Ovule (containing female gametophyte, or embryo sac) Egg Micropyle (2) The pollen tube discharges two sperm into the female gametophyte (embryo sac) within an ovule. Ovule Polar nuclei Egg Two sperm about to be discharged (3) One sperm fertilizes the egg, forming the zygote. The other sperm combines with the two polar nuclei of the embryo sac’s large central cell, forming a triploid cell that develops into the nutritive tissue called endosperm. Endosperm nucleus (3n) (2 polar nuclei plus sperm) Zygote (2n) (egg plus sperm) Figure 38.6

16. Development of Ovule and Endosperm • From Ovule to Seed, after double fertilization • Each ovule develops into a seed • The ovary develops into a fruit enclosing the seed(s) • Endosperm Development, usually precedes embryo development • In most monocots and some eudicots, the endosperm stores nutrients that can be used by the seedling after germination • In other eudicots, the food reserves of the endosperm are completely exported to the cotyledons

17. Embryo Development • The first mitotic division of the zygote is transverse • Splitting the fertilized egg into a basal cell and a terminal cell Ovule Endosperm nucleus Integuments Zygote Zygote Terminal cell Proembryo Basal cell Suspensor Basal cell Cotyledons Shoot apex Seed coat Root apex Endosperm Suspensor Figure 38.7

18. Structure of the Mature Seed • The embryo and its food supply • Are enclosed by a hard, protective seed coat • In a common garden bean, a eudicot • The embryo consists of the hypocotyl, radicle, and thick cotyledons 種皮 上胚軸 Seed coat Epicotyl 下胚軸 Hypocotyl Radicle 胚根 子葉 Cotyledons (a) Common garden bean, a eudicot with thick cotyledons. The fleshy cotyledons store food absorbed from the endosperm before the seed germinates. Figure 38.8a

19. Seed coat Endosperm Cotyledons Epicotyl Hypocotyl Radicle • The seeds of other eudicots, such as castor beans • Have similar structures, but thin cotyledons 種皮 Seed coat Endosperm 胚乳 Cotyledons 子葉 Epicotyl 上胚軸 Hypocotyl 下胚軸 Radicle 胚根 (b) Castor bean, a eudicot with thin cotyledons. The narrow, membranous cotyledons (shown in edge and flat views) absorb food from the endosperm when the seed germinates. Figure 38.8b

20. The embryo of a monocot (單子葉) has a single cotyledon, a coleoptile, and a coleorhiza Pericarp fused with seed coat (種皮) Scutellum (cotyledon) (子葉) (胚乳) Endosperm (上胚軸) Epicotyl (芽鞘) Coleoptile (下胚軸) Hypocotyl Coleorhiza (根鞘) (胚根) Radicle (c) Maize, a monocot. Like all monocots, maize has only one cotyledon. Maize and other grasses have a large cotyledon called a scutellum. The rudimentary shoot is sheathed in a structure called the coleoptile, and the coleorhiza covers the young root. Figure 38.8c

21. From Ovary to Fruit • A fruit • Develops from the ovary • Protects the enclosed seeds • Aids in the dispersal of seeds by wind or animals

22. Carpels Ovary Flower Stamen Stigma Stamen Ovule Pineapple inflorescence Raspberry flower Pea flower Carpel (fruitlet) Stigma Each segment develops from the carpel of one flower Seed Ovary Stamen Pea fruit Raspberry fruit Pineapple fruit (b) Aggregate fruit. An aggregate fruit develops from many separate carpels of one flower (examples: raspberry, blackberry, strawberry). (c) Multiple fruit. A multiple fruit develops from many carpels of many flowers (examples: pineapple, fig). (a) Simple fruit. A simple fruit develops from a single carpel (or several fused carpels) of one flower (examples: pea, lemon, peanut). Figure 38.9a–c • Fruits are classified into several types • Depending on their developmental origin

23. Seed Germination (種子萌芽) • As a seed matures • It dehydrates (脫水) and enters a phase referred to as dormancy (休眠)

24. Seed Dormancy: 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 cues • From Seed to Seedling (從種子到幼苗) • Germination of seeds depends on the physical process called imbibition (浸潤) • The uptake of water due to low water potential of the dry seed

25. The radicle (胚軸) is the first organ to emerge from the germinating seed • In many eudicots, a hook forms in the hypocotyl (下胚軸), and growth pushes the hook above ground Foliage leaves (初生葉) (上胚軸) Cotyledon Hypocotyl Epicotyl (上胚軸) Cotyledon Cotyledon (子葉) (上胚軸) Hypocotyl Hypocotyl (上胚軸) Seed coat (種皮) Radicle (胚根) (a)Common garden bean. In common garden beans, straightening of a hook in the hypocotyl pulls the cotyledons from the soil. Figure 38.10a

26. Foliage leaves Coleoptile Coleoptile Radicle • Monocots (單子葉植物) • Use a different method for breaking ground when they germinate • The coleoptile (芽鞘) • Pushes upward through the soil and into the air (b) Maize. In maize and other grasses, the shoot grows straight up through the tube of the coleoptile. Figure 38.10b

27. Concept 38.3: Many flowering plants clone(複製) themselves by asexual reproduction • Many angiosperm species reproduce both asexually and sexually (無性及有性) • Sexual reproduction • Generates the genetic variation that makes evolutionary adaptation possible • Asexual reproduction in plants • Is called vegetative reproduction(營養繁殖)

28. Mechanisms of Asexual Reproduction (無性生殖的機制) • Fragmentation (裂片) • Is the separation of a parent plant into parts that develop into whole plants • Is one of the most common modes of asexual reproduction • In some species, the root system of a single parent gives rise to many adventitious shoots that become separate shoot systems Figure 38.11

29. Vegetative Propagation (營養繁殖) and Agriculture • Humans have devised various methods for asexual propagation of angiosperms • Clones from cuttings (切枝、切條) • Many kinds of plants are asexually reproduced from plant fragments called cuttings • Grafting (架接、接枝) • In a modification of vegetative reproduction from cuttings • A twig or bud from one plant can be grafted onto a plant of a closely related species or a different variety of the same species

30. Test-Tube Cloning (試管複製) and Related Techniques • Plant biologists have adopted in vitro methods to create and clone novel plant varieties. (a) Just a few parenchyma cells from a carrot gave rise to this callus, a mass of undifferentiated cells. (b) The callus differentiates into an entire plant, with leaves, stems, and roots. Figure 38.12a, b

31. Figure 38.13 50 m • In a process called protoplast fusion (原生質體融合) • Researchers fuse protoplasts, plant cells with their cell walls removed, to create hybrid plants Vacuole Chloroplast

32. Concept 38.4: Plant biotechnology is transforming agriculture • Plant biotechnology has two meanings: • It refers to innovations in the use of plants to make products of use to humans • It refers to the use of genetically modified organisms(GMO, 基因改造生物) in agriculture and industry

33. Artificial Selection (人工選擇; 人擇) • Humans have intervened • In the reproduction and genetic makeup of plants for thousands of years • Maize (玉米) • Is a product of artificial selection by humans • Is a staple (xxxxx) in many developing countries, but is a poor source of protein • Interspecific hybridization of plants (植物的種間雜交) • Is common in nature and has been used by breeders, ancient and modern, to introduce new genes Figure 38.14

34. Genetically modified rice GM papaya Ordinary rice Figure 38.15 Figure 38.16 Reducing World Hunger and Malnutrition (營養不良) • Genetically modified (GM) plants • Have the potential of increasing the quality and quantity of food worldwide

35. The Debate over Plant Biotechnology (植物生物技術的爭議) • There are some biologists, particularly ecologists • Who are concerned about the unknown risks associated with the release of 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 • Possible Effects on Nontarget Organisms • Many ecologists are concerned that the growing of GM crops might have unforeseen effects on nontarget organisms

36. The Debate over Plant Biotechnology (植物生物技術的爭議) • Addressing the Problem of Transgene Escape • Perhaps the most serious concern that some scientists raise about GM crops is the possibility of the introduced genes escaping from a transgenic crop into related weeds through crop-to-weed hybridization (作物雜草雜交) • Despite all the issues associated with GM crops • The benefits should be considered

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