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Plant Responses to Signals IV

Plant Responses to Signals IV . Photomorphogenesis Circadian Rhythms Gravitropism. http://sunflower.bio.indiana.edu/~rhangart/plantsinmotion.html. Germination. Stem elongation (inhibition). Action Spectra. Action Spectrum , graph of the magnitude of a biological response to light,

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Plant Responses to Signals IV

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  1. Plant Responses to Signals IV Photomorphogenesis Circadian RhythmsGravitropism http://sunflower.bio.indiana.edu/~rhangart/plantsinmotion.html

  2. Germination Stem elongation (inhibition) Action Spectra • Action Spectrum, • graph of the magnitude of a biological response to light, • as a function of wavelength.

  3. hypothesis Germination Molecular Switch…looking for a photoreceptor, …look for a photo-reversible pigment.

  4. Germination Absorption vs. Action Spectra…looking for a photoreceptor,

  5. red light FR light Phytochromephotoreceptor molecule dimer

  6. Quantity, Time, Quality. Phytochromephotoreceptor molecule See Fig. 38.5

  7. Phytochrome Location Phtyochrome is a cytosolic protein.

  8. Phytochrome…has multiple functions, • Seed Germination, • Flowering time (photoperiodism), • Entraining (setting) the biological clock, • End of day, • Stem elongation, • Leaf Expansion, • Pigment synthesis.

  9. Short-day plants, …night breaks inhibit flowering. Photoperiodism…flowering times, Long-day plants, …night breaks induce flowering. See Fig 38.3, 4

  10. …use photoreversibility to establish phytochrome function. Phytochrome…photoperiodism, Fig 38.3

  11. Germination Stem elongation (inhibition) Phytochrome absorbtion spectra, …the wavelengths absorbed by specific pigments. not phytochrome

  12. Stem elongation (inhibition) Cryptochromes • blue light photoreceptors (I), • …evolved from a light dependent DNA repair enzyme, • ...across phylogeny, these proteins have been used for many functions, • ranging from blue-light-dependent development in plants, • blue-light-mediated phase shifting of the circadian clock in insects, • to a core circadian clock component in mammals.

  13. Phototropins…mediate phototropism, blue light photoreceptors II • …contribute to stem, root and leaf movements in response to directional information, • to maximize light gathering capacity, • and to minimize light damage at high irradiances. Phototropism action spectrum

  14. Photomorphogenesis Functions Concept Map Photoreversible Phytochrome Cryptochrome Signal transduction Photoperiodism Phototropin Action Spectra, Absorption spectra

  15. Circadian Rhythms • Relating to, or exhibiting approximately 24-hour periodicity, • circa around + dies day. • Internal Biochemical Oscillators, • found in all eukaryotes, • eubacteria as well. sleep movements Fig 39.21

  16. amplitude • <- Period (24h) -> Circadian Rhythms …of response, Circadian processes continue even if light (or dark) is continuous... Entrainment • …amplitude and period entrainment is continuous, • - allows fine control.

  17. ~ 480 of 8,000 (tested) genes are under circadian control, • ~1,500 (estimated) Arabidopsis genes, or ~6% follow circadian cycles of expression.

  18. Photosynthesis genes... Secondary metabolism (wood, defense).

  19. shoots, …are negatively gravitropic. roots, …are positively gravitropic. Gravitropism … the gravity directed growth processes that direct root and shoot orientation during a plants life-cycle, • about 1.7%, or roughly 500 genes, are transcribed in Arabidopsis when it is re-oriented 90o.

  20. Gravitropic Set Point 180o 90o 0o Plant organs orient themselves to the gravity vector.

  21. Moss http://www.biosci.ohio-state.edu/~plantbio/Sacklab/timelapse.html Starch Statolith Hypothesis Re-orientation of heavy starch grains signals gravity vector. Fig 39.25

  22. Possible Essay Questions • Describe the process and evolutionary advantage of de-etiolation in plants. Include in your discussion the function of phytochrome, second messengers, and two possible mechanisms of response. Also include the functions of some proteins and hormones produced during de-etiolation. • Auxin plays many roles within a plant. One of it's chief functions is to stimulate cell expansion. Describe it's journey from where it is synthesized to where it is perceived, and the response. • Angiosperm species account for more than three-quarters of all plant life on Earth. What characteristics/adaptations enable this plant type to be successful (structurally, at the cell and tissue level, reproductive advantages, etc.)? • Describe the "relationship" that forms between rhizobium bacteria and their legume hosts. How does it benefit either party? Are there any relative drawbacks to the symbiosis? How can you (physically) tell if a plant has been infected with rhizobium (at macro and micro levels)? • Several hormones act to counterbalance each other in plant physiology. Select two such hormones, describe the effects they have individually on an organism, and explain how they balance each other's effects on a plant.

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