Biology. Chapter 27. Plant Reproduction and Development. Concepts and Applications 9e Starr Evers Starr. Cengage Learning 2015

Transcription

1 Biology Concepts and Applications 9e Starr Evers Starr Chapter 27 Plant Reproduction and Development

2 27.1 What Are the Structure and Function of Flowers? Flowers: reproductive structures of angiosperms Parts of a flower: Stamens: consists of an anther and often a filament Anther: produces pollen Pollen grains: Immature male gametophyte of a seed plant

3 What Are the Structure and Function of Flowers? (cont d.) Parts of a flower (cont d.) Carpel: consists of an ovary, stigma, and often a style Stigma: upper part of a carpel; adapted to receive pollen Ovary: enlarged base of a carpel, inside which one or more ovules form Ovule: structure inside an ovary in which a female gametophyte forms

4 ANIMATION: Flower parts

5 Pollination Pollination: arrival of pollen on a receptive stigma Pollen is often transferred to a stigma by a pollination vector (e.g., animal or wind) Animal pollination vectors are called pollinators

6 Pollination (cont d.) Non-reproductive traits (e.g., petal color) are evolutionary adaptations that attract coevolved pollinators Flower traits tend to reflect the abilities and preferences of their pollinator allies Example: Bee-pollinated flowers tend to be fragrant, with UV-reflecting pigments in their petals

7 Pollination (cont d.)

8 Pollination (cont d.) A B C

9 27.2 How Does Sexual Reproduction Occur in a Flowering Plant? Life cycle of flowering plants is dominated by the sporophyte Diploid spore-producing plant body that grows by mitotic cell divisions of a fertilized egg Spores that form by meiosis inside a sporophyte s flowers develop into haploid gametophytes, which produce gametes

10 ANIMATION: Floral structure and function To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

11 How Does Sexual Reproduction Occur in a Flowering Plant? (cont d.) Steps of sexual reproduction: 1. Female gametes begin to form when an ovule starts to grow in the ovary 2. An ovule cell undergoes meiosis, forming four haploid megaspores 3. One megaspore undergoes three rounds of mitosis; a cell with eight haploid nuclei forms 4. A seven-celled embryo sac (the female gametophyte) forms

12 How Does Sexual Reproduction Occur in a Flowering Plant? (cont d.) Steps of sexual reproduction (cont d.): 5. Male gametes emerge inside anthers as diploid, spore-producing cells form by mitosis; four pollen sacs form 6. Each pollen sac cell undergoes meiosis; four haploid microspores form 7. Microspores differentiate into pollen grains 8. Pollen grains enter dormancy: period of suspended metabolism

13 How Does Sexual Reproduction Occur in a Flowering Plant? (cont d.) Steps of sexual reproduction (cont d.): 9. A pollen grain that lands on a receptive stigma germinates: outer cell develops into a tubular outgrowth called a pollen tube 10. A pollen grain s inner cell undergoes mitosis to produce two sperm cells (male gametes) The pollen tube grows toward the embryo sac of a female gametophyte 11.Two sperm cells are released into the ovule

14 ANIMATION: Eudicot life cycle To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

15 How Does Sexual Reproduction Occur in a Flowering Plant? (cont d.) Double fertilization: one sperm cell fuses with the egg, and a second sperm cell fuses with the endosperm mother cell Endosperm: nutritive tissue in the seeds of flowering plants

16 27.3 How Do Seeds and Fruits Develop? The embryo sporophyte forms: The zygote develops into an embryo, and the triploid cell develops into endosperm As the embryo matures, the outer cell layers of the ovule develop into a tough seed coat Seed: embryo sporophyte of a seed plant packaged with nutritive tissue inside a protective coat

17 Fruits Fruit: seed-containing mature ovary, often with fleshy tissues that develop from the ovary wall Simple fruits: derived from one ovary Example: pea pods, acorns, and shepherd s purse Aggregate fruits: derived from separate ovaries of one flower that mature as a cluster Example: blackberry, strawberry

18 Fruits (cont d.) tissue derived from ovary wall carpel wall seed enlarged receptacle A B

19 Fruits (cont d.) The function of a fruit is to protect and disperse seeds Fruits adapted for certain dispersal vectors Wind dispersion: lightweight fruits with breeze-catching specializations Water dispersion: fruits float; water-repellent outer layers Animal dispersion: fruits with hooks or spines; attract animals for consumption

20 Fruits (cont d.) A B C

21 27.4 What Happens During Plant Development? An embryonic plant complete with shoot and root apical meristems forms as part of a seed As the seed matures, the embryo may dry out and enter a period of dormancy Dormant embryo can rest in its protective seed coat for many years

22 What Happens During Plant Development? (cont d.) seed coat endosperm cells cotyledon(s) coleoptile plumule hypocotyl radicle

23 Breaking Dormancy Seed dormancy allows germination to occur when conditions in the environment are most likely to support growth Other than the presence of water, the triggers for germination differ by species Examples: physical disruption, exposure to freezing temperatures, bright light, smoke, and burning

24 Breaking Dormancy (cont d.) Start of germination: Water causes the seed s internal tissues to swell, forcing the seed coat to rupture Hydrolysis enzymes break down stored starches into sugar subunits; fuels rapid cell division End of germination: First part the embryonic root, or radicle, breaks out of the seed coat

25 After Germination Pattern of early growth that occurs after germination varies Example: in monocots a coleoptile protects a growing embryonic shoot of monocots In eudicot seedlings, the primary shoot is not protected by a coleoptile

26 ANIMATION: Plant development To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

27 After Germination (cont d.) Pattern of development in typical eudicot: 1. Radicle emerges from the seed, followed by the hypocotyl 2. Hypocotyl bends into a hook shape as it lengthens 3. Bent hypocotyl pulls the cotyledons upward through the soil until it reaches the surface

28 After Germination (cont d.) Pattern of development in typical eudicot (cont d.): 4. Exposure to light causes the hypocotyl to straighten 5. Primary leaves emerge from between the cotyledons and begin photosynthesis 6. Cotyledons typically undergo a period of photosynthesis before shriveling

29 27.5 How Do Plants Reproduce Asexually? Most flowering plants can reproduce asexually by vegetative reproduction New roots and shoots grow from extensions or pieces of a parent plant

30 How Do Plants Reproduce Asexually? (cont d.) B A

31 Agricultural Applications Some plants form new roots and shoots from nodes on a stem Other plants must be grafted A cutting must be fused with the tissues of another plant Examples: apple trees, grapevines Tissue culture propagation: plant cells (typically from meristem) are induced to form embryos

32 Agricultural Applications (cont d.)

33 27.6 What Regulates Growth and Development in Plants? Plant cells coordinate developmental activities by communicating with one another via plant hormones Extracellular signaling molecules that exert their effects at very low concentrations

34 27.7 What Are Some Effects of Auxin and Cytokinin? Auxin: plant hormone that causes lengthening Plays central role in growth by coordinating the effects of other hormones Cytokinin: plant hormone that promotes cell division in shoot apical meristem and cell differentiation in root apical meristem Often interacts antagonistically with auxin

35 What Are Some Effects of Auxin and Cytokinin? (cont d.) When a shoot is lengthening at the tip, its lateral buds are typically dormant, an effect called apical dominance Auxin maintains apical dominance by regulating production, transport, and degradation of cytokinin in a stem

36 What Are Some Effects of Auxin and Cytokinin? (cont d.) auxin auxin cytokinin auxin A B C D E

37 27.8 How Does Gibberellin Affect Plant Growth? Gibberellin: plant hormone that promotes growth in flowering plants Causes a stem to lengthen between the nodes by inducing cell division and elongation Gibberellin is also involved in slowing the aging of leaves and fruits, breaking dormancy in seeds, germination of seeds, and flowering

38 How Does Gibberellin Affect Plant Growth? (cont d.)

39 How Does Gibberellin Affect Plant Growth? (cont d.) aleurone endosperm embryo gibberellin amylase A B glucose C

40 27.9 What Are Some Effects of Abscisic Acid and Ethylene? Abscisic acid (ABA): plant hormone involved in stomata function and stress responses; inhibits germination Named because of its role in abscission: process by which a plant sheds leaves or other parts

41 What Are Some Effects of Abscisic Acid and Ethylene? (cont d.) ABA facilitates stomata closing by initiating nitric oxide release; in turn this allows Ca 2+ to enter the cytoplasm of guard cells Increase in Ca 2+ triggers malate and Cl - to be pumped out of the cells Gated transport proteins open, allowing K + to exit the cells Water flows out via osmosis; stomata close as the guard cells collapse

42 What Are Some Effects of Abscisic Acid and Ethylene? (cont d.)

43 Ethylene Ethylene: plant hormone involved in stomata function and stress responses; inhibits germination Positive feedback loops produce large amounts of ethylene required for intermittent processes: Germination, defense responses, abscission, fruit formation, and ripening

44 Ethylene (cont d.)

45 27.10 How Do Environmental Cues Trigger Growth Response in Plants? Plants respond to environmental stimuli by adjusting their growth Each plant optimizes its opportunities for photosynthesis, absorption of water and nutrients, reproduction, and other factors that affect its fitness

46 Environmental Triggers Tropism: growth adjustment in response to environmental stimuli Types of tropism: Gravitropism: plant growth in a direction influenced by gravity Phototropism: plant growth in a direction influenced by light Thigmotropism: plant growth in a direction influenced by contact

47 Environmental Triggers (cont d.) B A C

48 Environmental Triggers (cont d.) statoliths A B

49 Environmental Triggers (cont d.)

50 Environmental Triggers (cont d.) A B C

51 27.11 How Do Plants Sense and Respond to Recurring Environmental Change? Circadian rhythm: cycle of biological activity that repeats every twenty-four hours or so Example: bean plant holds its leaves horizontally during the day; folds them at night Circadian rhythms are driven by interconnected feedback loops involving transcription factors

52 ANIMATION: Rhythmic leaf movements To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

53 How Do Plants Sense and Respond to Recurring Environmental Change? (cont d.)

54 How Do Plants Sense and Respond to Recurring Environmental Change? (cont d.) Pigments provide light input into internal circadian clocks Phytochromes: absorb red light; causes structure to change from an inactive to an active form Cryptochromes: absorb blue and UV light

55 Seasonal Change Photoperiodism: an organism s response to changes in the length of day relative to night Flowering is a photoperiodic response in many species Long-day plants (e.g., irises) flower when hours of darkness are less Short-day plants (e.g., chrysanthemums) flower when hours of darkness are greater

56 ANIMATION: Flowering response experiments To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE

57 Seasonal Change (cont d.) Vernalization: stimulation of flowering in spring by prolonged exposure to low temperature in winter Yearly cycles of abscission and dormancy are photoperiodic responses Example: ripening chestnuts emit ethylene that stimulates abscission of the fruits and nearby leaves

58 Seasonal Change (cont d.) A B

59 27.12 How Do Plants Respond to Stress? Plant stressors: Biotic: imposed by pathogens and herbivores Abiotic: caused by nonliving environmental conditions Plants have defenses against biotic and abiotic stressors Example: wounding a leaf triggers the production of many protective molecules ABA, hydrogen peroxide, ethylene, jasmonic acid

60 How Do Plants Respond to Stress? (cont d.) A B C

61 How Do Plants Respond to Stress? (cont d.) A pathogen that penetrates a plant s epidermis triggers a large surge of hydrogen peroxide and nitric oxide Causes cells in the infected region to commit suicide This hypersensitive response can prevent a pathogen from spreading to other parts of the plant

62 How Do Plants Respond to Stress? (cont d.)

63 How Do Plants Respond to Stress? (cont d.) Systemic acquired resistance: inducible whole-body resistance to a wide range of pathogens and abiotic stressors