Plant Responses to Internal and External Signals Chapter 31.
Plant Responses to Signals IV
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Transcript of Plant Responses to Signals IV
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Plant Responses to Signals IV
PhotomorphogenesisCircadian Rhythms
Gravitropism
http://sunflower.bio.indiana.edu/~rhangart/plantsinmotion.html
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• Action Spectrum,
– graph of the magnitude of a biological response to light,
– as a function of wavelength.
Action Spectra
Germination
Stem elongation(inhibition)
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Molecular Switch…looking for a photoreceptor,
Germinationhypothesis
…look for a photo-reversible pigment.
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Absorption vs. Action Spectra…looking for a photoreceptor,
Germination
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Phytochromephotoreceptor molecule
dimer
redlight
FRlight
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Phytochromephotoreceptor molecule
Quantity,Time,Quality.
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Phytochrome Location
Phtyochrome is a cytosolic protein.
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Phytochrome…has multiple functions,
• Seed Germination,
• Flowering time (photoperiodism),
• Entraining (setting) the biological clock,
• End of day,
• Stem elongation,
• Leaf Expansion,
• Pigment synthesis.
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Photoperiodism…flowering times,
Long-day plants,
…night breaks induce flowering.
Short-day plants,
…night breaks inhibit flowering.
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Phytochrome…photoperiodism,
…use photoreversibility to establish phytochrome function.
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Phytochrome
absorbtion spectra,
…the wavelengths absorbed by specific pigments.
Germination
Stem elongation(inhibition)
not phytochrome
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Cryptochromesblue 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.
Stem elongation(inhibition)
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Phototropins…mediate phototropism,
…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
blue light photoreceptors II
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Concept Map
Phytochrome
Action Spectra, Absorption spectra
Photoperiodism
Photomorphogenesis
Cryptochrome
Phototropin
PhotoreversibleFunctions
Signal transduction
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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
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Circadian Rhythms
<- Period (24h) ->
amplitude
Entrainment
Circadian processes continue even if light (or
dark) is continuous...
…amplitude and period entrainment is continuous,
- allows fine control.
…of response,
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~ 480 of 8,000 (tested) genes are under circadian control,
• ~1,500 (estimated) Arabidopsis genes, or ~6% follow circadian cycles of expression.
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Photosynthesis genes...
Secondary metabolism (wood, defense).
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Gravitropism
… the gravity directed growth processes that direct root and shoot orientation during a plants life-cycle,
roots,
…are positively gravitropic.
shoots,
…are negatively gravitropic.
– about 1.7%, or roughly 500 genes, are transcribed in Arabidopsis when it is re-oriented 90o.
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Gravitropic Set Point
0o
90o
180o
Plant organs orient themselves to the gravity vector.
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Starch Statolith Hypothesis
Re-orientation of heavy starch grains signals gravity vector.
http://www.biosci.ohio-state.edu/~plantbio/Sacklab/timelapse.htmlMoss