Presentation is loading. Please wait.

Presentation is loading. Please wait.

Plant Response to Signals Ch 39. Plant Response  Stimuli & a Stationary Life  animals respond to stimuli by changing behavior  move toward positive.

Similar presentations


Presentation on theme: "Plant Response to Signals Ch 39. Plant Response  Stimuli & a Stationary Life  animals respond to stimuli by changing behavior  move toward positive."— Presentation transcript:

1 Plant Response to Signals Ch 39

2 Plant Response  Stimuli & a Stationary Life  animals respond to stimuli by changing behavior  move toward positive stimuli  move away from negative stimuli  plants respond to stimuli by adjusting growth & development

3 Signal Transduction Pathway model  signal triggers receptor  receptor triggers internal cellular messengers & then cellular response  receptor  signal pathway (2° messengers)  response What kinds of molecules are the receptors?

4 Signal Transduction Pathway example 1. Light signal is detected by the phytochrome receptor, which then activates at least 2 signal transduction pathways 2. One pathway uses cGMP as a 2nd messenger to activate a protein kinase. The other pathway involves increases in cytoplasmic Ca 2+ that activates a different protein kinase. 3. Both pathways lead to expression of genes for proteins that function in greening response of plant.

5 Signal Transduction Pathway example 1. Light signal is detected by the phytochrome receptor, which then activates at least 2 signal transduction pathways 2. One pathway uses cGMP as a 2nd messenger to activate a protein kinase. The other pathway involves increases in cytoplasmic Ca 2+ that activates a different protein kinase. 3. Both pathways lead to expression of genes for proteins that function in greening response of plant.

6 Plants do not have brains  Or nervous systems for that matter,  So how do they communicate with itself and coordinate beneficial responses?

7 Plant hormones  Chemical signals that coordinate different parts of an organism  only tiny amounts are required  produced by 1 part of body  transported to another part  binds to specific receptor  triggers response in target cells & tissues

8 Plant hormones  auxins  cytokinins  gibberellins  abscisic acid  ethylene

9 Hormones in review:  AUXINS __ Promote cellular elongation __ by softening of cell walls __ Involved in phototropism __ Involved in geotropism __ Involved in apical dominance  CYTOKININS __ Promotes lateral growth_ growth in size of leaf cells __ Stimulate cell division (hence name) __ Release buds from apical dominance  GIBERELLINS __ seasonal growth___ Stimulate cell elongation __ Produce bolting in biennials __ Stimulate production of starch digestion enzymes in some seeds  ABSCISIC ACID __ opposite of giberellins__causes slow down or “cut off” of growth__Promotes stomatal closure __ __ Promotes seed and bud dormancy _  ETHYLENE __ Promotes ripening of fruit

10 Response to light: Phototropism  Growth towards light  Hormone: Auxin  asymmetrical distribution of auxin, moves away from sunny side of stem (-ve phototropism, -ve gravitropism)  cells on darker side elongate faster than cells on brighter side

11 Apical dominance  Controls cell division & differentiation  axillary buds do no grow while apical bud exerts control shoot root

12 Figure 39.8 Cross-linking polysaccharides Cell wall–loosening enzymes Cellulose microfibril Expansin CELL WALL Plasma membrane CYTOPLASM Plasma membrane Cell wall Nucleus Cytoplasm Vacuole H2OH2O HH HH HH HH HH HH HH HH HH ATP Cell elongation in response to auxin: the acid growth hypothesis

13 Gibberellins  Family of hormones  over 100 different gibberellins identified  Effects  fruit growth  seed germination plump grapes in grocery stores have been treated with gibberellin hormones while on the vine

14 Abscisic acid (ABA)  Effects  slows growth  seed dormancy  high concentrations of Abscisic acid  germination only after ABA is inactivated down or leeched out  survival value: seed will germinate only under optimal conditions  light, temperature, moisture  drought tolerance  rapid stomate closing

15 Ethylene  Ethylene is a hormone gas released by plant cells  Multiple effects  response to mechanical stress  triple response  slow stem elongation  thickening of stem  curvature to stem growth  leaf drop (like in Fall)  apoptosis  fruit ripening

16 Apoptosis & Leaf drop: combination of hormones  Ethylene & auxin  many events in plants involve apoptosis (pre-programmed cell death)  death of annual plant after flowering  differentiation of xylem vessels  loss of cytosol  shedding of autumn leaves What is the evolutionary advantage of loss of leaves in autumn?

17 Fruit ripening  Adaptation  hard, tart fruit protects developing seed from herbivores  ripe, sweet, soft fruit attracts animals to disperse seed  Ethylene  triggers ripening process  breakdown of cell wall  softening  conversion of starch to sugar  sweetening  positive feedback system  ethylene triggers ripening  ripening stimulates more ethylene production

18 Applications  Truth in folk wisdom…..  one bad apple spoils the whole bunch  ripening apple releases ethylene to speed ripening of fruit nearby  Ripen green bananas by bagging them with an apple  Climate control storage of apples  high CO 2 storage = reduces ethylene production

19 Plant stimuli

20 Flowering Response  Triggered by photoperiod  relative lengths of day & night  night length—“critical period”— is trigger Short-day plantsLong-day plants Plant is sensitive to red light exposure What is the evolutionary advantage of photoperiodism? Synchronizes plant responses to season

21 Circadian rhythms  Internal (endogenous) 24-hour cycles Morning glory 4 O’clock NoonMidnight

22 Response to gravity  How does a sprouting shoot “know” to grow towards the surface from underground?  environmental cues?  roots = positive gravitropism  shoots = negative gravitropism  settling of statoliths (dense starch grains) may detect gravity

23 Response to touch  Thigmotropism Mimosa (Sensitive plant) closes leaves in response to touch Caused by changes in osmotic pressure = rapid loss of K + = rapid loss of H 2 O = loss of turgor in cells

24 Plant defenses  Defenses against herbivores

25 Plant defenses  Defenses against herbivores Parasitoid wasp larvae emerging from a caterpillar coevolution

26 Any Questions??


Download ppt "Plant Response to Signals Ch 39. Plant Response  Stimuli & a Stationary Life  animals respond to stimuli by changing behavior  move toward positive."

Similar presentations


Ads by Google