Plant Responses to Signals IV

1
Plant Responses to Signals IV

• Photomorphogenesis
• Circadian RhythmsGravitropism

http//sunflower.bio.indiana.edu/rhangart/plantsi
nmotion.html
2
Signal Transductiongeneral
Second messengers, - kinase cascades, -
calcium concentration, - etc.
Receptors, - G-protein linked, - enzyme
linked, - ion channel, - etc.
Responses, - gene expression (/-), -
membrane dynamics, - metabolism -
cytoskeleton - etc.
Signals, - hormone, - light, -
temperature, - gravity, - etc.
Fig. 39.2
3
no ethylene no triple response.
active
inactive
?
induces transcription,
no transcription
erf ethylene response factor.
4
Photomorphogenesis

• Light is used by plants as a signal, as well as
  an energy source,
• quantity,
• quality (wavelength),
• direction,
• duration.

• Germination (/-)
• Stem length (-)
• Leaf expansion ()
• Flowering (/-)
• Phototropism (/-)
• Stomatal opening ()
• Chloroplast development ()
• Pigment synthesis ()
• and more...

5
Action Spectra

• Action Spectrum,
• graph of the magnitude of a biological response
  to light,
• as a function of wavelength.

6
Molecular Switchlooking for a photoreceptor,
look for a photo-reversible pigment.
Fig. 39.18
7
Phytochromephotoreceptor molecule
dimer
Fig. 39.19
8
Phytochromephotoreceptor molecule
Quantity, Time, Quality.
Fig. 39.20
9
Phytochrome Location
Phtyochrome is a cytosolic protein.
10
Phytochromehas 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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Photoperiodismflowering times,
Long-day plants, night breaks induce flowering.
Fig 39.22
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Phytochromephotoperiodism,
Fig 39.22
13
Phytochrome
absorbtion spectra, the wavelengths absorbed by
specific pigments.
not phytochrome
14
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.

15
Phototropinsmediate phototropism,

• blue light photoreceptors II,
• contribute to stem, root and leaf movements in
  response to directional information,
• also contributes to the alignment of
  chloroplasts within mesophyll cells,
• to maximize light gathering capacity,
• and to minimize light damage at high
  irradiances.

Phototropism action spectrum
16
Concept Map
Functions
Photoreversible
Phytochrome
Cryptochrome
Photoperiodism
Phototropin
Action Spectra
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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
Fig 39.21
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Circadian Rhythms
of response,
Circadian processes continue even if light (or
dark) is continuous...
Entrainment
amplitude and period entrainment is
continuous, - allows fine control.
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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.

20
Photosynthesis genes...
Secondary metabolism (wood, defense).
21
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.

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Gravitropic Set Point
180o
90o
0o
Plant organs orient themselves to the gravity
vector.
23
Starch Statolith Hypothesis
http//www.biosci.ohio-state.edu/plantbio/Sacklab
/timelapse.html

• Re-orientation of heavy starch grains signals
  gravity vector.

Fig 39.25
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Final

• All material since Lecture 11 (Reproduction),
• lecture, book and other assigned readings (i.e.
• Review 5 pm Monday, (will post room on WEB),
• Final, here in this room
• Tuesday 11/9, 1030 1230.

25
Assigned Essays

• Explain the importance of auxin in plants. How it
  is signaled, what are some of its function, where
  is it made, how is it transported? Give an
  example how it interacts with other hormones.
• Why would a plant want to prevent self
  pollination? Discuss two mechanisms used by
  angiosperms to avoid self fertilization.
• Give examples of heterospory and homospory and
  explain the differences between the two,
  mentioning the evolutionary significance.
• Describe how phase changes are used by
  developmental biologists to uncover biological
  processes.
• Describe how plants use light and hormones to
  influence the germination of the seed.
• What is phytochrome?

26
Assigned Essays

• Explain the importance of auxin in plants. How it
  is signaled, what are some of its function, where
  is it made, how is it transported? Give an
  example how it interacts with other hormones.
• Why would a plant want to prevent self
  pollination? Discuss two mechanisms used by
  angiosperms to avoid self fertilization.
• Give examples of heterospory and homospory and
  explain the differences between the two,
  mentioning the evolutionary significance.
• Describe how phase changes are used by
  developmental biologists to uncover biological
  processes.
• Describe how plants use light and hormones to
  influence the germination of the seed.
• What is phytochrome?