1. Angiosperm Reproduction
Chapter 38
Angiosperm Reproduction

2. Angiosperms have 3 unique Features:
Flowers
Fruits
Double Fertilization (by 2 sperm)

3. REPRODUCTIVE VARIATIONS

4. Pollination: transfer pollen from anther to stigma

5. “Pin” and “thrum” flower types reduce self-fertilization
Some plants are self-pollinated
Cross-pollinated plants:
Self-incompatibility: plant rejects own pollen or closely related plant
Maximize genetic variation
Stigma
Pin flower
Anther
with
pollen
Thrum flower
“Pin” and “thrum” flower types reduce self-fertilization

6. The development of a plant embryo

7. Fruit Egg cell  plant embryo Ovules inside ovary  seeds
Ripe ovary  fruit
Fruit protects enclosed seed(s)
Aids in dispersal by water, wind, or animals

8. Types of Fruit

9. Seeds Mature seed  dormancy (resting) Low metabolic rate
Growth & development suspended
Resumes growth when environmental conditions suitable for germination

12. Germination
Seed take up water (imbibition)  trigger metabolic changes to begin growth
Root develops  shoot emerges  leaves expand & turn green (photosynthesis)
Very hazardous for plants due to vulnerability
Predators, parasites, wind

13. (Vegetative Reproduction)
Plant Reproduction
Sexual
Asexual
(Vegetative Reproduction)
Flower  Seeds
Runners, bulbs, grafts, cuttings
vegetative (grass), fragmentation, test-tube cloning
Genetic diversity
Clones
More complex & hazardous for seedlings
Simpler (no pollinator needed)
Advantage in unstable environments
Suited for stable environments

14. Asexual reproduction in aspen trees
Test-tube cloning of carrots

15. Humans Modify Crops Artificial selection of plants for breeding
Plant Biotechnology:
Genetically modified organisms
“Golden Rice”: engineered to produce beta-carotene (Vit. A)
Bt corn: transgenic – expresses Bt (bacteria) gene  produces protein toxic to insects
Biofuels – reduce CO2 emissions
Biodiesel: vegetable oils
Bioethanol: convert cellulose into ethanol

16. Plant Responses to Internal and External Signals
Chapter 39
Plant Responses to Internal and External Signals

17. Concept 39.1: Signal transduction pathways link signal reception to response
A potato left growing in darkness produces shoots that look unhealthy, and it lacks elongated roots
These are morphological adaptations for growing in darkness, collectively called etiolation
After exposure to light, a potato undergoes changes called de-etiolation, in which shoots and roots grow normally
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18. (a) Before exposure to light (b)
Figure 39.2
Figure 39.2 Light-induced de-etiolation (greening) of dark-grown potatoes.
(a) Before exposure to light
(b)
After a week’s exposure to natural daylight

19. A potato’s response to light is an example of cell- signal processing
The stages are reception, transduction, and response
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20. Activation of cellular responses
Figure 39.3
CELL WALL
CYTOPLASM 1
Reception 2
Transduction 3
Response
Relay proteins and
Activation of cellular responses
second messengers
Receptor
Figure 39.3 Review of a general model for signal transduction pathways.
Hormone or environmental stimulus
Plasma membrane

21. Reception
Internal and external signals are detected by receptors, proteins that change in response to specific stimuli
In de-etiolation, the receptor is a phytochrome capable of detecting light
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22. Transduction
Second messengers transfer and amplify signals from receptors to proteins that cause responses
Two types of second messengers play an important role in de-etiolation: Ca2+ ions and cyclic GMP (cGMP)
The phytochrome receptor responds to light by
Opening Ca2+ channels, which increases Ca2+ levels in the cytosol
Activating an enzyme that produces cGMP
© 2011 Pearson Education, Inc.

23. 1 Reception CYTOPLASM Plasma membrane Phytochrome Cell wall Light
Figure 1
Reception
CYTOPLASM
Plasma membrane
Phytochrome
Cell wall
Light
Figure 39.4 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response.

24. Protein kinase 1 Protein kinase 2
Figure 1
Reception 2
Transduction
CYTOPLASM
Plasma membrane
cGMP
Protein kinase 1
Second messenger
Phytochrome
Cell wall
Protein kinase 2
Light
Figure 39.4 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response.
Ca2 channel
Ca2

25. De-etiolation (greening) response proteins
Figure 1
Reception 2
Transduction 3
Response
Transcription factor 1
CYTOPLASM
NUCLEUS
Plasma membrane
cGMP
Protein kinase 1 P
Second messenger
Transcription factor 2
Phytochrome P
Cell wall
Protein kinase 2
Transcription
Light
Translation
Figure 39.4 An example of signal transduction in plants: the role of phytochrome in the de-etiolation (greening) response.
Ca2 channel
De-etiolation (greening) response proteins
Ca2

26. Response
A signal transduction pathway leads to regulation of one or more cellular activities
In most cases, these responses to stimulation involve increased activity of enzymes
This can occur by transcriptional regulation or post- translational modification
© 2011 Pearson Education, Inc.

27. Post-Translational Modification of Preexisting Proteins
Post-translational modification involves modification of existing proteins in the signal response
Modification often involves the phosphorylation of specific amino acids
Kinases: phosphorylate other molecules
Phosphotases: opposite
The second messengers cGMP and Ca2+ activate protein kinases directly
© 2011 Pearson Education, Inc.

28. Transcriptional Regulation
Specific transcription factors bind directly to specific regions of DNA and control transcription of genes
Some transcription factors are activators that increase the transcription of specific genes
Other transcription factors are repressors that decrease the transcription of specific genes
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29. De-Etiolation (“Greening”) Proteins
De-etiolation activates enzymes that
Function in photosynthesis directly
Supply the chemical precursors for chlorophyll production
Affect the levels of plant hormones that regulate growth
© 2011 Pearson Education, Inc.

30. Experiments with Light and the coleoptile
Conclusion: Tip of coleoptile senses light  some signal was sent from tip to elongating region of coleoptile

31. Excised tip placed
on agar block
Growth-promoting
chemical diffuses
into agar block
Agar block
with chemical
stimulates growth
Offset blocks
cause curvature
Control
(agar block
lacking
chemical)
has no
effect
Cells on darker side elongate faster than cells on brighter side AUXIN = chemical messenger that stimulates cell elongation

32. Cross-linking polysaccharides Cell wall–loosening enzymes Expansin
Figure 39.8
Cross-linking polysaccharides
Cell wall–loosening enzymes
Expansin
CELL WALL
Cellulose microfibril
H2O H
Plasma membrane H H
Cell wall H H H H H
Figure 39.8 Cell elongation in response to auxin: the acid growth hypothesis.
Nucleus
Plasma membrane
Cytoplasm
ATP H
Vacuole
CYTOPLASM

33. Hormones: chemical messengers that coordinate different parts of a multicellular organism
Important plant hormones:
Auxin – stimulate cell elongation  phototropism & gravitropism (high concentrations = herbicide)
Cytokinins – cell division (cytokinesis) & differentiation
Gibberellins – stem elongation, leaf growth, germination, flowering, fruit development
Abscisic Acid – slows growth; closes stomata during H2O stress; promote dormancy
Ethylene – promote fruit ripening (positive feedback!); involved in apoptosis (shed leaves, death of annuals)

34. The effects of gibberellin on stem elongation and fruit growth

35. Ethylene Gas: Fruit Ripening
Canister of ethylene gas to ripen bananas in shipping container
Untreated tomatoes vs. Ethylene treatment

36. Plant Movement Tropisms: growth responses  SLOW
Phototropism – light (auxin)
Gravitropism – gravity (auxin)
Thigmotropism – touch
Turgor movement: allow plant to make relatively rapid & reversible responses
Venus fly trap, mimosa leaves, “sleep” movement

37. Positive gravitropism in roots: the statolith hypothesis.

38. Thigmotropism: rapid turgor movements by Mimosa plant  action potentials

39. Plant Responses to Light
Plants can detect direction, intensity, & wavelenth of light
Phytochromes: light receptors, absorbs mostly red light
Regulate seed germination, shade avoidance

40. Biological Clocks Circadian rhythm: biological clocks
Persist w/o environmental cues
Frequency = 24 hours
Phytochrome system + Biological clock = plant can determine time of year based on amount of light/darkness

41. Night length is a critical factor!
Photoperiodism: physiological response to the relative length of night & day (i.e. flowering)
Short-day plants: flower when nights are long (mums, poinsettia)
Long-day plant: flower when nights are short (spinach, iris, veggies)
Day-neutral plant: unaffected by photoperiod (tomatoes, rice, dandelions)
Night length is a critical factor!

42. How does interrupting the dark period with a brief exposure to light affect flowering?

44. Plant responses to stress

45. Flooding (O2 deprivation):
Drought (H2O deficit):
close stoma
release abscisic acid to keep stoma closed
Inhibit growth
roll leaves  reduce SA & transpiration
deeper roots
Flooding (O2 deprivation):
release ethylene  root cell death  air tubes formed to provide O2 to submerged roots

46. Excess Salt: Heat: Cold: cell membrane – impede salt uptake
produce solutes to ↓ψ - retain H2O
Heat:
evap. cooling via transpiration
heat shock proteins – prevent denaturation
Cold:
alter lipid composition of membrane (↑unsat. fatty acids, ↑fluidity)
increase cytoplasmic solutes
antifreeze proteins

47. Herbivores: Pathogens: physical (thorns) chemicals (garlic, mint)
recruit predatory animals (parasitoid wasps)
Pathogens:
1st line of defense = epidermis
2nd line = pathogen recognition, host-specific