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. Antipodal cells 2 polar nuclei Egg Synergid cells
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 structure that provides nutrients to developing embryo
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: B. Transduction/amplification C. Response
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

26. Fig. 11.9

27. Fig

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

29. Fig. 11.9

30. 2. Mechanisms: a. Transcriptional regulation – activated transcription
factors bind to DNA & control transcription of specific
genes

31. Fig. 18.8

32. Fig. 18.9

33. b. Post – translational modification of proteins – by
phosphorylation by protein kinases

34. Fig. 39.4

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

36. 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

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

39. 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

40. 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!

41. 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

42. (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.

43. Fig. 39.9

44. 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

45. (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.

46. 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

47. e. Counteracts first 3 growth hormones
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

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

49. 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

50. 2. Effects a. Fruit ripening b. Leaf abscission
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.

51. Fig

52. 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

53. Fig 39.13 Triple response to mechanical stress

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

55. Examples of Plant Responses

56. V. Plant Responses: A. Phototropism B. Photoperoidism
C. Gravity - gravitropism
D. Touch/ mechanical stimuli - thigmotropism
E. Responses to stress
F. Responses to herbivores & pathogens

57. A. Phototropism 1. Definition Plants detect light’s direction,
intensity, & wavelength
2. Receptors:
a. Blue light – light-induced stomatal opening
b. Phytochromes
i. Red light receptors
ii. Most important
iii. Exist in 2 reversible forms: Pr & Pfr. Relative
amounts in plant stimulates various responses

58. Fig. 39.19 Phytochrome switching

59. 3. Responses a. Inhibition of internode elongation
b. Development of proper leaf shape
c. Increase in number of stomata per leaf
d. Increase in amount of chlorophyll
e. Decrease in apical dominance
f. Increased accumulation of carotenoid pigments in tomatoes
g. Membrane permeability
h. Seed germination
i. Spore germination
j. Chloroplast movement
k. Inter-node extension, Hypocotyl hood formation, Leaflet movement, Geotropic sensitivity, Anthocyanin synthesis,
l. Shade avoidance
m. Circadian rhythms

60. (Aside) Circadian Rhythms and Clocks
1. Circadian rhythm = a physiological cycle with a frequency of about 26 hours that persists even when an organism is sheltered from environmental cues.
2. all eukaryotes
3. Plant examples: stomatal opening/closing, production of PSN enzymes (Others?)
4. Mechanism: ???? Phytochromes receptors may “train” the biological clock to 24 hours.

61. B. Photoperiodism 1. Definition
a. Photoperiodism is a physiological response to day length.
b. Synchronization of plant events according to seasons
c. Plants detect the time of year by the photoperiod (the relative lengths of night and day).

62. a. Night length is the important factor (continuous hours of darkness)
2. Mechanisms (Trends)
a. Night length is the important factor (continuous hours of darkness)
b. Short–day (Long–night) plants - flower in late summer, fall, and winter.
c. Long–day (short–night) plants - flower in late spring and summer.
d. Day–neutral plants are unaffected by photoperiod.

63. Fig 39.21

64. b. Some plants flower after a single exposure to the proper photoperiod.
c. Some require several successive days of the proper photoperiod to bloom.
d. Still others respond to photoperiod only if they have been previously exposed to another stimulus. (e.g. vernalization)
e. Leaves detect the photoperiod – send signals to buds to produce flowers.

65. C. Gravitropism 1. Definition
a. Gravity provides stimulus for plants to grow up
out of ground, no matter the seed orientation in the
soil.
b. Gravitational pull on plant cell causes starch
grains to settle to bottom - stimulates an asymmetric
production of auxin in the cell

66. 2. Mechanisms a. Thus different rates of cell elongation on opposite
sides of the root /shoot.
b. Root grows down & shoot grow up

67. Fig 39.25

68. D. Thigmotropism 1. Definition 2. Mechanisms
a. Directional growth in response to “touch”
Ex. Vines winding around fence, tree
b. Stimulus activates genes that affect cell wall
properties Ex. Mimosa pudica

69. D. Stress (Stressotropism)
1. Drought
a. Increase in ABA keeps guard cells closed
b. Thus plant growth slows because cells can’t
elongate or photosynthesize
2. Flooding
a. Ethylene stimulates some root cells to die
(apoptosis) to create air tubes in the roots

70. 3. Salt stress a. Problem: roots can lose water because soil water
has lower potential
b. Response: root cells produce extra organic solutes
within the cell to create lower potential inside

71. 4. Heat stress 5. Cold stress
a. Production of heat-shock proteins which prevent cell enzymes from denaturation
5. Cold stress
a. Problem: cell membranes become less fluid and transport becomes difficult
b. Response: cell replaces membrane fats with fats that remain fluid at lower temperatures

72. 6. Pests a. Morphological adaptations like thorns
b. Production of toxic compounds when bitten
c. Production of chemicals that attract predator to the herbivore – ex. Parasitic wasps
d. Production of anti-microbial compounds
e. Seal off the pathogen and initiate cell death to remove it

73. Fig 39.28

74. Breathe deep and cherish moments before they wisp away.