Angiosperm Reproduction and Assorted Topics

1. Angiosperm Reproduction and Assorted Topics

2. I.The Angiosperm Life Cycle Fig 30.10

3. Fig 38.2

4. A. Male Gametophyte (Pollen) • 1. Anther is composed of pollen sacs (male • sporangium). • 2. Inside pollen sac: 2n cells called • microsporocytes undergo meiosis to form 4 haploid • microspores. • Each microspore divides by mitosis to make 2 cells: • a. Generative cell – will make sperm • b. Tube cell – will make pollen tube • The 2 cells enclosed in thick wall  pollen grain

5. B. Female Gametophyte (Embryo Sac) 1. Ovule = female sporangium 2. 2n cell in ovule (megasporocyte) divides by meiosis to form 4 haploid megaspores. 3. Only one megaspore survives and divides by mitosis 3 times to make 8 haploid nuclei.

6. 4. Supporting Cells a. Synergids – attract and guide pollen tube to the egg b. Antipodal cells – unknown function c. 2 polar nuclei – eventually fuse with a sperm to make the 3n endosperm

7. Embryo Sac = female gametophyte Antipodal cells 2 polar nuclei Egg Synergid cells

8. Fig 38.3

9. II. Angiosperm Reproduction A. Pollination 1. Pollen grain lands on stigma (= pollination) 2. Generative cell divides by mitosis to form 2 sperm cells 3. Tube cell forms pollen tube 4. Sperm travel down pollen tube and enter embryo sac 5. Double fertilization

10. 5. Double Fertilization • a. Egg + sperm  zygote • b. 2 polar nuclei + sperm  • 3n nucleus that becomes the • endosperm Fig 38.5

11. B. Maturation 1. Endosperm begins to divide to form structure that provides nutrients to developing embryo 2. Embryo divides to form cotyledons (= seed leaves) and meristems 3. Ovule is now a seed – dehydrates & becomes dormant (low metabolism, no growth). 4. Ovary tissues divide & mature into fruit

12. Embryo Development (Eudicot) Fig 38. 7

13. C. Germination • 1. Dormant seed becomes a seedling • 2. Seed needs proper conditions to break dormancy • 3. Steps: • a. Water uptake by seed causes expansion • b. Embryo begins to grow • c. Enzymes digest endosperm & transfers • nutrients to embryo • d. Radicle (embryo root) emerges • e. Hypocotyl (embryo shoot) raises cotyledons • above ground • f. True leaves form & PSN begins

14. Fig 38.9

15. III. Asexual Reproduction A. Why? B. How?

16. Plant Responses to Internal and External Signals

17. I. Introduction • A. General Ideas for example, plants can…. • 1. send signals between different parts of the plant • 2. track the time of day and the time of year • 3. sense and respond to gravity and the direction or wavelength of light

18. B. How do they respond? • 1. by adjusting their growth pattern and development Example = Etiolation

19. 2. Hormone = chemical signal produced by one part of a plant and translocated to other parts where it triggers a response in target cells and tissues 3. Environmental stimuli cause increases or decreases in levels/ratios of hormones in the plant

20. II. Cell Signaling: • A. Reception • B. Transduction/amplification • C. Response

21. Fig. 39.3

22. A. Reception • 1. Receptor proteins (on cell membrane) receive the signal (hormone ) & undergo conformational change • 2. Absorption of a specific wavelength of light by a intracellular pigment

23. B. Transduction/Amplification 1. Membrane Bound a. G-protein b. Tyrosine Kinases • 2. Secondary Messengers • a. cAMP or cGMP. • b. Kinases/Phophotases. • c. Calcium

24. Examples of Second Messengers: • G proteins – active when GTP bound. Activate: • Cyclic nucleotides – cAMP or cGMP. Activate: • Protein kinases – enzymes that phosphorylate & thus • activate other proteins such as transcription factors. • Cascade of protein kinases amplify the signal. • Calcium – a mineral that can bind to activate protein • kinases.

25. Fig. 11.11

26. Fig. 11.9

27. Fig. 11.13

28. C. Response 1. Amplified signal induces the regulation of a specific cellular activity. Fig. 11.9

29. 2. Mechanisms: • a. Transcriptional regulation – activated transcription • factors bind to DNA & control transcription of specific • genes Fig. 18.9 Fig. 18.8

30. b. Post – translational modification of proteins – by • phosphorylation by protein kinases Fig. 39.4

31. c. Rapid, regulating physiology: • i. stimulation of stomatal closing • d. Slow, gene expression. • i. Control of development by affecting cell division, elongation, and differentiation.

32. III. Types of Plant Responses • A. Tropism – growth responses toward or • away from a stimulus (Photo. or Gravi.) • B. Nastic response – non-growth response • Ex. Venus flytrap mechanism; turgor • changes • C. Morphogenic response – morphological • response (change in shape, growth) Ex. • Onset of flowering

33. IV. Six Major Plant Hormones A. Auxin (IAA) B. Cytokinins C. Gibberellins (GA) D. Brassinosteroids E. Abscisic acid (ABA) F. Ethylene

35. A. Auxin 1. Production Site 2. Effects a. Cell elongation & differentiation b. Root growth c. Branching d. Apical dominance e. Fruit development f. Phototropism & gravitropism

36. Auxin can also: g. Stimulate roots to grow from cuttings h. Be used as an herbicide (very high levels of auxin inhibits growth) i. Stimulate fruit development without pollination  seedless fruits!

37. B. Cytokinin 1. Production Site 2. Effects a. Root growth & differentiation b. Cell division (cytokinesis) & differentiation c. Germination d. Prevents leaf senescence/aging (florists spray cytokinins to keep flowers fresh) e. Control of apical dominance

38. (Aside) Apical Dominance 1. Auxin travels down stem & inhibits axillary bud growth causing the shoot to lengthen. 2. Cytokinins travel up from roots to stimulate axillary bud growth. 3. If SAM removed, auxin concentration drops & cytokinins stimulate axillary buds to grow. 4. Lower bud thus grow before higher ones since they are closer to the cytokinin source than the auxin source.

39. Fig. 39.9

40. C. Gibberellins 1. Production Site 2. Effects a. Fruit growth b. Release of some seeds and buds from dormancy c. Stem elongation (act with auxin to acidify cell wall) d. Bolting of inflorescence

41. (Aside) Dormancy and Germination 1. High concentration of gibberellins in seeds & embryo. 2. The release of gibberellins signals seeds to break dormancy and germinate. 3. Imbibed water (& other environmental cues) stimulates gibberellin release.

42. D. Abscisic Acid (ABA) • 1. Production Site • 2. Effects • a. Initiation of dormancy/ inhibition of germination • b. Stimulates production of proteins that allow seed • to withstand dehydration • c. Water washes ABA away, gibberellins stimulate • germination • d. Inhibits growth

43. e. Counteracts first 3 growth hormones. Ratio of ABA to others determines outcome • f. Stomatal closure during water stress • g. Root water stress stimulates ABA production, travels up to leaves to “warn” them to close stomata before wilting occurs

44. E. Brassinosteroids 1. Production Site 2. Effects a. Inhibit root growth & leaf abscission b. Promote xylem differentiation

45. F. Ethylene 1. Production Site a. The only gaseous hormone. b. Diffuses through air spaces between plant cells. c. Produced in response to stresses: drought, flood, injury, infection

46. 2. Effects • a. Fruit ripening • Conversion of starches to sugars • Fruit picked green, then gassed with ethylene to induce • ripening • b. Leaf abscission • Leaves drop off plant in response to water stress, seasonal • change • Ethylene stimulates enzymes to digest cell walls of the • abscission layer of petiole.

47. Fig. 39.15

48. c. Apoptosis = programmed cell death Death of leaves in Fall, yearly death of annuals Ethylene stimulates enzymes that break down cells d. Triple response to mechanical stress There’s a rock in the way! Ethylene production stimulates: slowing of stem growth, stem thickens, stem curves, & then grows horizontally Once past the rock, ethylene production declines & plant can grow up again

49. Fig 39.13 Triple response to mechanical stress

50. G. Minor Plant Hormones 1. Strigolactones a. Production site b. Effects Seed germination, control apical dominance, attract mycorrhizal fungi 2. Florigen a. Production site b. Effects Flowering