Photorespiration: * Rubisco catalyze its oxygenation ability omnipresent, even in anaerobic, autotrophic bacteria when exposed to oxygen * Loss of CO.
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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
Three organellesCarbon flow 22C13C+CO
2
75%Nitrogen flow no changedOxygen flow 3 O2/2 RuBP
Malate-OAA shuttle supply NADH
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
ROS
Photorespiration depends on the photosynthetic electron transport system
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
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
Cyanobacterial CO2 concentrating mechanism
— high homologous to the Rheus, a protein in erythrocytes
The C4 carbon cycleKranz (wreath) cells: present two distinct chloroplast-containing cells,
mesophyll and bundle sheath cells
spatial
OAA
Calvin cycle
sugarcane
Flaveria australasica
Poa sp
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
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.
Kranz anatomy: mesophyll and bundle-sheath cells carbon concentrating mechanism / suppressed photorespiration
plasmodesmata
Photosynthetic Carbon assimilation reduction
Borszczowia aralocaspica
Bienertia cycloptera
Chloroplasts containing rubisco are near mitochondria with NAD-ME
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