The Dark reaction aka the lightindependent reaction

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Summary light reactions
lumen
stroma
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Cyclic electron flow produces more ATP
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Two major problems for light reactions

• Too little light
• Too much light

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• Photoprotection via pigments acting as
  antioxidants

http//sciencenow.sciencemag.org/cgi/content/full/
2005/121/3
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Can light reactions be made more efficient?

• In marginal habitats, more photoprotective
  pigments could be genetically induced
• In optimal habitats, fewer photoprotective
  pigments and more chlorophyll a could be
  genetically induced

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The Dark reactionaka the light-independent
reaction
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(No Transcript)
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Major player Rubisco
http//www.biologie.uni-hamburg.de/lehre/bza/1rxo/
e1rxoe.htm
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Figure 10.17 The Calvin cycle (Layer 1)
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Figure 10.17 The Calvin cycle (Layer 2)
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Figure 10.17 The Calvin cycle (Layer 3)
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Summary of input needed to produce 1 molecule
glucose

• 48 photons of red light
• 6 molecules CO2
• From non-cyclic photophosphorylation 12 ATP
• From non-cyclic electron flow 12
  NADPH
• From cyclic photophosphorylation 6 ATP

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The two faces of Rubisco
Janus by Jim Westermark
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Photorespiration

• When O2 levels high relative to CO2, rubisco
  combines with O2
• Up to 50 of carbon potentially fixed is lost in
  photorespiration
• Most serious at high temperatures
• Possible advantages?

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Two solutions to photorespiration C4 and CAM
C4 spatial separation CAM temporal separation
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Most C4 plants have Kranz anatomy
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But not all . . .
Scanning electron microscopy (left panel) and
immunological localization of Rubisco (right
panel) in a photosynthetic cell of the single
cell C4 species Suaeda aralocaspica showing the
Rubisco-containing chloroplasts (orange) are
restricted to the proximal end of cell (right
panel).
Scanning electron micrograph (left panel) of a
photosynthetic cell in the single cell C4 species
Bienertia cycloptera showing that only the
chloroplasts in the central cytoplasmic
compartment contain Rubisco (orange) (right
panel). (Images by Elena Voznesenskaya and Vince
Franceschi)
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C3 vs C4 vs CAM

• Numbers of species/individuals
• Photorespiration
• Water use efficiency
• Typical habitats
• Energetics

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Useful links
General website good review, links http//www.em
c.maricopa.edu/faculty/farabee/BIOBK/BioBookPS.htm
l Need to improve rice yield, etc International
Rice Research Institute