1 / 32

Chapter 39.

Chapter 39. Plant Response. Plant Reactions. 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. What mechanism causes this response?.

shika
Download Presentation

Chapter 39.

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 39. Plant Response

  2. Plant Reactions • 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. What mechanism causes this response? grown in dark 1 week exposure to light

  4. 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?

  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 Ca2+ that activates a different protein kinase. 3. Both pathways lead to expression of genes for proteins that function in greening response of plant.

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

  7. Plant hormones • auxins • cytokinins • gibberellins • brassinosteroids • abscisic acid • ethylene

  8. Went 1926 Phototropism • Growth towards light

  9. Auxin • Indolacetic acid (IAA) • stimulates cell elongation • near apical meristems • enhances apical dominance • classical explanation of phototropism • asymmetrical distribution of auxin • cells on darker side elongate faster than cells on brighter side

  10. Zones of meristem growth shoot root

  11. Polarity of auxintransport • Auxin picks up H+ between cells & is neutralized • Neutral auxin passes through membrane • Cellular pH 7 causes auxin to ionize & is trapped in cell • Auxin stimulates proton pump • Auxin leaves through carriers

  12. Auxin response Acid growth hypothesis

  13. Cytokinins • Family of hormones • modified forms of adenine • produced in roots, fruits & embryos • Effects • control of cell division & differentiation • enhances apical dominance • interaction of auxin & cytokinins

  14. Gibberellins • Family of hormones • over 100 different gibberellins identified • Effects • stem elongation • fruit growth • seed germination

  15. Brassinosteroids • Steroids • Effects • similar to auxins • cell elongation & division in shoots & seedlings

  16. Abscisic acid (ABA) • Effects • slows growth • seed dormancy • high concentrations of ABA • 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

  17. Ethylene • Ethylene is a gas released by plant cells • Multiple effects • response to mechanical stress • triple response • slow stem elongation • thickening of stem • curvature to horizontal growth • apoptosis • leaf abscission • fruit ripening

  18. Apoptosis & Leaf abscission What is the evolutionary advantage of loss of leaves in autumn? • Balance of ethylene & auxin • many events in plants involve pre-programmed cell death • death of annual plant after flowering • differentiation of xylem vessels • loss of cytosol • shedding of autumn leaves

  19. Fruit ripening • Hard, tart fruit protects developing seed from herbivores • Ripe, sweet, soft fruit attracts animals to disperse seed • burst of 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

  20. 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 CO2 storage = reduces ethylene production

  21. Responses to light • Photomorphogenesis • effect of light on plant growth • Light detection • intensity • direction • wavelength • blue-light receptors • phytochromes (red-light receptors) Why does it make “biological sense” that red & blue light have greater effects on plants response that other wavelengths?

  22. Phytochrome photoreceptors • Molecular switch reaction to red light • conversion of Pr Pfr in sunlight stimulates germination, flowering, branching… • conversion of Pfr Pr in dark inhibits response, & stimulates other responses: growth in height Light induced Chromophore Photorecptor Kinase activity Phytochrome Phytochrome Response: Vertical growth

  23. Practical Application • Why do you plant lettuce seed by scattering them on the ground instead of burying seed? • What is the evolutionary advantage to lettuce seeds?

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

  25. Is there a flowering hormone? • Plant on left is induced to flower & then grafted onto plant on right • plant on right is triggered to flower What can you conclude?

  26. Circadian rhythms • Internal (endogenous) 24-hour cycles 4 O’clock Noon Midnight Morning glory

  27. Responses to gravity • How does a sprouting shoot “know” to grow towards the surface from underground? • environmentalcues? • roots = positive gravitropism • shoots = negative gravitropism • settling of statoliths (dense starch grains) may detect gravity

  28. Responses 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 H2O = loss of turgor in cells

  29. Plant defenses • Defenses against herbivores

  30. Plant defenses • Defenses against herbivores Parasitoid wasp larvae emerging from a caterpillar

  31. Plant defenses • Defenses against pathogens

  32. Help Me!!!

More Related