photorespiration: * rubisco catalyze its oxygenation ability omnipresent, even in anaerobic,...
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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 organellesCarbon flow 22C13C+CO
2
75%Nitrogen flow no changedOxygen flow 3 O2/2 RuBP
Malate-OAA shuttle supply NADH
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Web Topics 8.6
[gas] µM = Pgas 106/ V0
In vitro vs. In vivo
Solubility of CO2 and O2 as a function of temperature
Pgas: partial pressure; : absorption coefficient
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
[CO2]inter (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:
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
0.03% CO2 / 21% O2
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Cyanobacterial CO2 concentrating mechanism
— high homologous to the Rheus, a protein in erythrocytes
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The C4 carbon cycleKranz (wreath) cells: present two distinct chloroplast-containing cells,
mesophyll and bundle sheath cells
spatial
OAA
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Calvin cycle
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sugarcane
Flaveria australasica
Poa sp
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The C4 photosynthetic pathway: Hatch and Slack
Gramineae (corn, millet, sorghum, sugarcane);
Chenopodiaceae (Atriplex); Cyperaceae (sedges).
external
vascular
NADP-ME: in chloroplastNAD-ME: in mitochondriaPEP carboxykinase: in cytosol
plasmodesmataspecific translocators
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Web Topic 8.7 (?)
Three variations of C4 metabolism
The form of transportation
The manner of decarboxylation
Aspartate aminotransferase
PEP carboxykinase
Alanine aminotransferase
(1) maize, crab grass, sugarcane, sorghum;
(2) pigweed, millet;
(3) guinea grass.
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Kranz anatomy: mesophyll and bundle-sheath cells carbon concentrating mechanism / suppressed photorespiration
plasmodesmata
Photosynthetic Carbon assimilation reduction
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Borszczowia aralocaspica
Bienertia cycloptera
Chloroplasts containing rubisco are near mitochondria with NAD-ME