Ch. 39 Plant Responses to Internal and External Signals

Transcription

1 Ch. 39 Plant Responses to Internal and External Signals Feb 13 7:03 PM 1

2 Essential Question: How do plants respond to internal and external stimuli? Feb 13 7:06 PM 2

3 plants use signal transduction pathways to respond to stimuli etiolation plant morphological adaptations to growth in darkness ex. potato produces long spindly stems if in the dark for a long time, penetrate the soil de etiolation (greening) changes a plant shoot undergoes in the presence of sunlight elongation of stem slows leaves expand roots start to elongate shoot produces chlorophyll Feb 13 7:08 PM 3

4 general model of signal transduction receptor proteins that receive a stimulus ex. phytochrome a photoreceptor functions in the cytoplasm as a light detector Feb 13 7:17 PM 4

5 Transduction second messengers small, internally produced chemicals that transfer and amplify the signal from the receptor to other proteins that cause a response role of phytochrome in greening process Feb 13 7:21 PM 5

6 Response a regulation of a cell activity two mechanisms a signaling pathway activates an enzyme 1. stimulating transcription of mrna for the enzyme (transcription regulation) transcription factors bind to regions of DNA and control transcription) positive and negative transcription factors (increase and decrease transcription respectively) 2. activating existing enzymes (post translational modification) modifying the proteins by phosphorylation protein kinase cascade can turn genes on or off protein phosphatases dephosphorylate proteins to "switch off" genes Feb 13 7:25 PM 6

7 role of phytochrome in greening process Feb 15 9:17 AM 7

8 Proteins that are transcribed or activated during de etiolation process: 1. enzymes needed for photosynthesis 2. enzymes for making chemical precursors for chlorophyll production 3. affect hormone levels Hormones are chemical signals that affect different parts of an organism chemicals produced by one part of the organism and then transported to another part and triggers a response only needed on small amounts to have an effect control plant growth by affecting the division, elongation, and differentiation of cells Feb 13 7:34 PM 8

9 plant people call hormones plant growth regulators because they can regulate locally Apr 6 8:13 AM 9

10 Tropism a growth response that results in curvatures of whole plant organs toward or away from a stimulus Phototropism light is stimulus positive phototropism moves towards light negative phototropism moves away from light Feb 13 7:40 PM 10

11 Survey of Plant Hormones Apr 16 7:01 AM 11

12 Auxin chemical substance that promotes elongation of coleoptiles natural auxin is indolacetic acid or IAA transported through parenchyma tissue, one cell to next moves only from shoot tip to base (called polar transport independent of gravity) How does it promote elongation? synthesized in apical meristem of shoot moves down to region of cell elongation stimulates plasma membrane's proton pumps (causes voltage) and lowers ph of cell wall low ph activates enzymes expansins break cross links between cellulose microfibrils so cells can elongate water enters cell increases turgor Feb 13 7:45 PM 12

13 cell elongation Feb 13 7:57 PM 13

14 Polar Auxin transport a chemiosmotic model Feb 15 9:23 AM 14

15 Auxins are used in vegetative propagation if a leaf or stem is cut and auxin is added to the cut end, adventitious roots form near cut surface also helps in branching of roots (lateral roots) Auxins as herbicides synthetic auxins used won't kill maize, turfgrass inactivate synthetic auxin kills eudicots (weeds) hormonal overdose Auxins in fruit formation induces cell division in vascular cambium and differentiates secondary xylem synthetic auxins promote fruit development without pollination Feb 13 7:59 PM 15

16 Cytokinins chemical substances that stimulate cytokinesis Zeatin most common type of cytokinin in plants stimulate cell division and differentiation in conjunction with auxin if auxin and cytokinin in equal amounts get callus growing if cytokinin levels are higher than auxin, shoot buds develop if auxin levels higher than cytokinin, roots form helps control apical dominance direct inhibition hypothesis auxin inhibits axillary buds cytokinins signal axillary buds to grow if auxin removed (terminal bud removed) plant gets bushier Feb 13 8:07 PM 16

17 anti aging effects inhibit protein breakdown stimulate RNA and protein synthesis slow leaf deterioration used as a spray to keep flowers fresh Apr 3 1:37 PM 17

18 Apical Dominance: with apical bud without apical bud Feb 15 9:26 AM 18

19 Giberillins effect: 1. stem elongation dwarf plants can grow to normal height if treated with giberillins Ex. in lettuce when giberillins present lets floral buds grow tall Feb 13 9:08 PM 19

20 2. Fruit Growth used in spraying of Thompson seedless grapes grow larger internodes elongate more space for grapes to grow 3. Germination embryo large source of giberillins when water absorbed in embryo, giberillins released seed germinates Feb 15 9:28 AM 20

21 Brassinosteroids induce cell elongation and division in stems retard leaf abscission promote xylem differentiation Abscisic Acid slows growth seed dormancy inhibit germination drought tolerance allows plants to withstand drought, causes stomata to close (loss of potassium ions) Feb 13 9:32 PM 21

22 Ethylene produced in Response to mechanical stress triple response if shoot is up against an obstacle if germinating a. slowing stem elongation b. thickens the stem c. curves the stem so grows horizontally Feb 13 10:02 PM 22

23 senescence = programmed death of certain cells or organs or the entire plant programmed cell death apoptosis leaf abscission causes cells to produce enzymes that digest cellulose in abscission layer (parenchyma cells) purpose prevent dessication during periods where water is scarce elements are salvaged from leaves and stored in stems until spring fruit ripening triggers ripening, ripening triggers more ethylene production (positive feedback) can get fruit to ripen faster if put in paper bag so ethylene gas accumulates Feb 15 10:31 AM 23

24 Plant Response to light used for photosynthesis used for photomorphogenesis changes in plant structure used for measurement of days/seasons plants detect presence, direction, intensity, and wavelength of light action spectrum wavelength spectrum that cause changes in plant Feb 14 11:14 AM 24

25 two major classes of photoreceptors 1. Blue light photoreceptors induces: a. phototropism by phototropin receptors b. opening of stomata by zeaxanthin c. slowing of hypocotyl elongation when seedling breaks ground by cryptochromes Feb 14 11:22 AM 25

26 2. Phytochromes important for germinating process, detect sunlight, and once plant is grown helps determine quality of light affected by red (660nm) and far red light (730nm) red light causes germination, far red light inhibits germination if plant is shaded, not getting red light but gets far red light programs plant to grow taller to reach sunlight helps plant keep track of seasons and days Feb 14 11:30 AM 26

27 Phytochrome regulation of lettuce seed germination Conclusion red light stimulates germination, far red inhibits germination. Final light is determining factor. Effects are reversible Feb 15 10:34 AM 27

28 Pfr is the active form or phytochrome it switches on the physiological and developmental responses in the plant Apr 6 3:47 PM 28

29 in lettuce seeds when exposed to red light Pr is converted to Pfr to stimulate germination phytochromes also provide information about quality of light during day P r = P fr for a dynamic equilibrium If a tree is shaded phtyochrome ratio shifts to P r because forest blocks out more red light than far red light causing a tree to grow taller direct sunlight increases P fr to stimulate branching and decrease vertical growth Apr 6 3:53 PM 29

30 Circadian Rhythms a physiological cycle of about 24 hours present in all eukaryotic organisms and continues even in the absence of external cues (like night and day) Ex. plant raising leaves during day daily production of certain photosynthesis proteins can get desynchronized if left in different conditions (ex. time zone changes in plane trips) Feb 14 11:36 AM 30

31 Photoperiodism a physiological response to a photoperiod (relative lengths of night and day) short day plants a plant that flowers (usually in late summer, fall or winter) only when the light period is shorter than a critical length ex. poinsettias, chrysanthemums, some soybeans Long day plants a plant that flowers (usually in late spring or early summer) only when the light period is longer than a critical length ex. spinach, radish, lettuce,iris Day neutral plants plants that are unaffected by photoperiod and flower when they reach maturity ex. tomatoes, rice, dandelions really based on length of continual darkness, not light Feb 14 11:46 AM 31

32 Chrysanthemums are short day plants normally bloom in fall to get them for Mother's Day growers turn one long night into two short days by using a flash of light Feb 14 11:55 AM 32

33 What is happening here? Apr 6 4:00 PM 33

34 vernalization using treatment of cold to induce flowering leaves detect the photoperiods and then signal (florigen hypothetical molecule for flowering still unidentified) buds to develop Feb 14 12:00 PM 34

35 Effect of gravity on plants gravitropism response to gravity positive grow towards ground (roots) negative grow away from ground (shoots) auxin is involved detect gravity by settling statoliths specialized plastids containing dense starch grains to lower portions of cells roots located in root cap Feb 14 12:04 PM 35

36 Mechanical Stimuli on plants thigmomorphogensis changes in the form that result from mechanical stimuli activates a signal transduction pathway that increases Calcium ions in cytosol thigmotropism directional growth in response to touch ex. tendrils of plants, "sensitive plant" due to loss of turgor pressure in joints of leaf once one leaflet touched causes and action potential through the other leaves Venus Flytrap have hairs that undergo action potentials Feb 14 12:10 PM 36

37 Rapid turgor movements by sensitive plant Feb 15 10:40 AM 37

38 Environmental Stresses 1. Droughtplant tries to conserve water by reducing transpiration a. leaf guard cells lose turgor so close stomata b. increases release of abscisic acid in leaf also helps close stomata c. inhibits growth of young leaves decreases surface area to minimize transpiration loss. d. leaves can roll up to decrease surface area reduces photosynthesis due to leaf changes e. roots inhibits growth of shallow roots lack of turgor f. causes growth of deep roots Feb 14 12:18 PM 38

39 2. Flooding plants suffocate due to lack of air spaces in soil mangroves have aerial roots and submerged roots ethylene causes root cells to undergo apoptosis (cell death) so creates air tubes in roots ("snorkels") Feb 14 12:50 PM 39

40 3. Salt stress lowers water potential of soil solution reduces water uptake sodium is toxic to plants in high concentrations halophyte plants are salt tolerant have salt glands that pump salt across leaf epidermis Feb 15 10:41 AM 40

41 4. Heat Stress dentures enzymes evaporative cooling by leaves closing stomata will reduce evaporative cooling synthesis of heat shock proteins help prevent denaturation 5. Cold Stress alter lipid concentration in membranes increase unsaturated fatty acids keep membranes fluid rapid chilling is more stressful than slow chilling some plants increase their solutes in cytoplasm so less chance of freezing Feb 14 1:07 PM 41

42 Defense against herbivores thorns chemicals (distasteful or toxic) ex. canavanine replaces arginine in proteins affects conformation of resulting protein insect dies have insects associated with them ex. parasitoid wasps attracted by leaf that has been damaged by caterpillar due to volatile compounds lay eggs in caterpillars that feed on plants larvae eat caterpillar during development volatile compounds also signal nearby plants so can activate defense genes Feb 14 1:14 PM 42

43 Defense response to herbivore involving parasitoid wasp Feb 15 10:42 AM 43

44 Defense against Pathogens epidermis and periderm pathogens can still enter if damaged via by stomata gene to gene recognition involves recognition of pathogen derived molecules by protein products of specific plant disease resistance genes (R genes) similar to our antibodies virulent pathogens pathogens that the plant can't defend against avirulent pathogens pathogens that invade plant, but don't kill it Feb 14 1:21 PM 44

45 gene to gene resistance of plants to pathogens Feb 15 10:43 AM 45

46 Responses to Pathogen invasions elicitors induce a defense response ex. oligosaccharins stimulate production of antimicrobial compounds called phytoalexins and PR proteins others signal infection to nearby cells increase lignin in cell walls to slow pathogen down hypersensitive response high production of phytoalexins and PR proteins that seal off infection systemic acquired resistance hypersensitive response "sounds the alarm" to the rest of the plant so stimulates production of phytoalexins and PR proteins in rest of plant nonspecific response to multiple pathogens salicylic acid activates systemic acquired resistance Feb 14 1:31 PM 46

47 Defense response against avirulent pathogen Feb 15 10:45 AM 47

48 Apr 16 7:18 AM 48