Photorespiration:

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Photorespiration

• Rubisco catalyze its oxygenation ability
• omnipresent, even in anaerobic, autotrophic
  bacteria when exposed to oxygen
• Loss of CO2 from cells
• Competition decrease the efficiency of
  photosynthesis
• Interconnection
• determined by the kinetic properties of
  rubisco, the concentration
• of substrates, and temperature
• C2 oxidative photosynthetic carbon cycle
  act as a scavenger operation to recover fixed
  carbon lost during photorespiration

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Three organelles Carbon flow 2?2C?1?3CCO2
75 Nitrogen flow no changed Oxygen flow 3
O2/2 RuBP
Malate-OAA shuttle supply NADH
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Web Topics 8.6gas µM Pgas ? ? ? 106/ V0In
vitro vs. In vivo
Pgas partial pressure ? absorption coefficient
Solubility of CO2 and O2 as a function of
temperature
T? ? tilt toward the C2 oxidative photosynthetic
cycle
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ROS
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Photorespiration depends on the photosynthetic
electron transport system
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The biological function of photorespirationis
under investigation
a protective, to dissipate excess ATP and
reducing power, especially under high
light intensity and low CO2inter (e.g.,
water stress) mutants lack glycerate
kinase, not viable in normal air linked
photorespiration to nitrate assimilation ? a
full understanding is still not at hand

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CO2-concentrating mechanisms
0.03 CO2 / 21 O2

• A. C4 photosynthetic carbon fixation (C4), in hot
  environment
• B. Crassulacean acid metabolism (CAM), in desert
  environment
• C. CO2 pumps at the plasma membrane.
• In aquatic plants, such as unicellular
  cyanobacteria and algae.
• In aquatic environment, CO2 low ?
  rubisco specificity activity low
• CO2-HCO3- pumps at the plasma membrane
  are induced,
• to accumulate inorganic carbon
• light energy provide ATP to uptake CO2
  and HCO3-
• carbonic anhydrase
• HCO3- H ? H2O CO2 ? Calvin
  cycle
• CO2 ?? suppress photorespiration

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Cyanobacterial CO2 concentrating mechanism
high homologous to the Rheus, a protein in
erythrocytes
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The C4 carbon cycle
spatial

• Kranz (wreath) cells present two distinct
  chloroplast-containing cells,
• mesophyll
  and bundle sheath cells

OAA
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Calvin cycle
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Poa sp
sugarcane
Flaveria australasica
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The C4 photosynthetic pathway Hatch and Slack

• Gramineae (corn, millet, sorghum, sugarcane)
• Chenopodiaceae (Atriplex) Cyperaceae (sedges).

external
plasmodesmata specific translocators
vascular
NADP-ME in chloroplast NAD-ME in
mitochondria PEP carboxykinase in cytosol
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Web Topic 8.7 (?) Three variations of C4
metabolism
The form of transportation The manner of
decarboxylation
(1) maize, crab grass, sugarcane, sorghum (2)
pigweed, millet (3) guinea grass.
Aspartate aminotransferase
PEP carboxykinase
Alanine aminotransferase
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Kranz anatomy mesophyll and bundle-sheath cells
carbon concentrating mechanism / suppressed
photorespiration
Photosynthetic Carbon assimilation
reduction
plasmodesmata
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Borszczowia aralocaspica
Bienertia cycloptera
Chloroplasts containing rubisco are near
mitochondria with NAD-ME