Ch. 39 Warm-UpCh. 39 Warm-Up1. Elaborate on the methods plants use to defend

themselves from pathogens and herbivores.

2. How do plants cope with:a. Floodingb. Droughtc. Heat stressd. 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 darkb. 14 hours light, 10 darkc. 14 hours light, 10 dark w/ flash of light

Ch. 39 Warm-UpCh. 39 Warm-UpMatch the following terms with the descriptions below:

A. AuxinB. CytokininsC. GibberellinsD. Abscisic AcidE. Ethylene

1. Inhibits growth, closes stomata during H2O stress2. Fruit ripening, promotes or inhibits growth3. Affects root growth, stimulates cell division &

growth, stimulates germination4. Stimulates stem elongation, root growth, fruit

development, photo- & gravitropism5. Promotes seed & bud germination, stem elongation,

flowering & development of fruit

What you must know: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.

Chapter 39Chapter 39Plant Responses to Internal and External Signals

Experiments with Light and the coleoptile

Excised tip placedon agar block

Growth-promotingchemical diffusesinto agar block

Agar blockwith chemicalstimulates growth

Offset blockscause curvature

Control(agar blocklackingchemical)has noeffect

Control

Cells on darker Cells on darker side elongate side elongate faster than cells faster than cells on brighter sideon brighter side

AUXINAUXIN = chemical = chemical messenger that messenger that stimulates cell stimulates cell elongationelongation

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 H2O stress; promote dormancy

5. Ethylene – promote fruit ripening (positive feedback!); involved in apoptosis (shed leaves, death of annuals)

The effects of The effects of gibberellin gibberellin on stem on stem elongation and fruit growthelongation and fruit growth

Ethylene gas: fruit ripeningEthylene gas: fruit ripening

Canister of ethylene gas to ripen bananas in shipping container

Untreated tomatoes vs. Ethylene treatment

Plant MovementPlant 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

Positive Positive gravitropismgravitropism in roots: the in roots: the statolith hypothesis.statolith hypothesis.

ThigmotropismThigmotropism: rapid turgor : rapid turgor movements by Mimosa plant movements by Mimosa plant action potentialsaction potentials

Plant Responses to LightPlant Responses to LightPlants can detect direction, intensity, &

wavelenth of lightPhytochromes: light receptors, absorbs

mostly red light◦Two forms: Pr (red light) and Pfr (far-red light)

◦Pr Pfr: switches depending on light in greatest supply

◦Pfr aids in detection of sunlight

◦Regulate seed germination,shade avoidance

Biological ClocksBiological 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

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

PhotoperiodismPhotoperiodism: physiological : physiological response to the relative length of response to the relative length of night & day (i.e. flowering)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)

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

Plant Response to StressPlant Response to Stress

Causes of stress:1. Drought (H2O deficit)

2. Flooding (O2 deprivation)

3. Salt excess4. Heat5. Cold6. Herbivores7. Pathogens

1. H2O deficit: close stoma release abscisic acid to keep stoma

closed Inhibit growth roll leaves reduce SA & transpiration deeper roots

2. Flooding (O2 deprivation): release ethylene root cell death

air tubes formed to provide O2 to submerged roots

3. Salt: cell membrane – impede salt uptake produce solutes to ↓ψ - retain H2O

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

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