1. Ch. 39 Warm-Up 1. Elaborate on the methods plants use to defend themselves from pathogens and herbivores. 2. How do plants cope with: a.Flooding b.Drought c.Heat stress d.Salt stress 3. If a long day plant needs at least 9 hours of dark, which scenario(s) will prevent flowering? a.16 hours light, 8 dark b.14 hours light, 10 dark c.14 hours light, 10 dark w/ flash of light

2. Ch. 39 Warm-Up Match the following terms with the descriptions below: A.Auxin B.Cytokinins C.Gibberellins D.Abscisic Acid E.Ethylene 1. Inhibits growth, closes stomata during H 2 O stress 2. Fruit ripening, promotes or inhibits growth 3. Affects root growth, stimulates cell division & growth, stimulates germination 4. Stimulates stem elongation, root growth, fruit development, photo- & gravitropism 5. Promotes seed & bud germination, stem elongation, flowering & development of fruit

3. What you must know: The three steps to a signal transduction pathway. The role of auxins in plants. How phototropism and photoperiodism use changes in the environment to modify plant growth and behavior. How plants respond to attacks by herbivores and pathogens.

4. Chapter 39 Plant Responses to Internal and External Signals

5. Experiments with Light and the coleoptile Conclusion: Tip of coleoptile responsible for sensing light, but growth occurred below tip  some signal was sent from tip to elongating region of coleoptile

6. 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 Control Cells on darker side elongate faster than cells on brighter side AUXIN = chemical messenger that stimulates cell elongation

7. Hormones: chemical messengers that coordinate different parts of a multicellular organism Important plant hormones: 1. Auxin – stimulate cell elongation  phototropism & gravitropism (high concentrations = herbicide) 2. Cytokinins – cell division (cytokinesis) & differentiation 3. Gibberellins – stem elongation, leaf growth, germination, flowering, fruit development 4. Abscisic Acid – slows growth; closes stomata during H 2 O stress; promote dormancy 5. Ethylene – promote fruit ripening (positive feedback!); involved in apoptosis (shed leaves, death of annuals)

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

10. Ethylene gas: fruit ripening Canister of ethylene gas to ripen bananas in shipping container Untreated tomatoes vs. Ethylene treatment

11. Plant Movement 1. Tropisms: growth responses  SLOW  Phototropism – light (auxin)  Gravitropism – gravity (auxin)  Thigmotropism – touch 2. Turgor movement: allow plant to make relatively rapid & reversible responses  Venus fly trap, mimosa leaves, “sleep” movement

12. Positive gravitropism in roots: the statolith hypothesis.

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

14. Plant Responses to Light Plants can detect direction, intensity, & wavelenth of light Phytochromes: light receptors, absorbs mostly red light ◦ Two forms: P r (red light) and P fr (far-red light) ◦ P r  P fr : switches depending on light in greatest supply ◦ P fr aids in detection of sunlight ◦ Regulate seed germination, shade avoidance

16. 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

17. Sleep movements of a bean plant. Caused by reversible changes in turgor pressure of cells on opposing sides of the pulvini, motor organs of the leaf.

18. 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!

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

21. Plant Response to Stress Causes of stress: 1.Drought (H 2 O deficit) 2.Flooding (O 2 deprivation) 3.Salt excess 4.Heat 5.Cold 6.Herbivores 7.Pathogens

22. 1. H 2 O deficit:  close stoma  release abscisic acid to keep stoma closed  Inhibit growth  roll leaves  reduce SA & transpiration  deeper roots 2. Flooding (O 2 deprivation):  release ethylene  root cell death  air tubes formed to provide O 2 to submerged roots

23. 3. Salt:  cell membrane – impede salt uptake  produce solutes to ↓ ψ - retain H 2 O 4. Heat:  evap. cooling via transpiration  heat shock proteins – prevent denaturation 5. Cold:  alter lipid composition of membrane ( ↑ unsat. fatty acids, ↑ fluidity)  increase cytoplasmic solutes  antifreeze proteins

24. 6. Herbivores:  physical (thorns)  chemicals (garlic, mint)  recruit predatory animals (parasitoid wasps) 7. Pathogens:  1st line of defense = epidermis  2nd line = pathogen recognition, host-specific