Photorespiration: * Rubisco catalyze its oxygenation ability omnipresent, even in anaerobic, autotrophic bacteria when exposed to oxygen * Loss of CO 2 from cells * Competition: decrease the efficiency of photosynthesis * Interconnection: determined by the kinetic properties of rubisco, the concentration of substrates, and temperature * C 2 oxidative photosynthetic carbon cycle: act as a scavenger operation to recover fixed carbon lost during photorespiration

Three organelles Carbon flow 2  2C  1  3C+CO 2 75% Nitrogen flow no changed Oxygen flow 3 O 2 /2 RuBP Malate-OAA shuttle supply NADH

Web Topics 8.6 [gas] µ M = P gas    10 6 / V 0 In vitro vs. In vivo Solubility of CO 2 and O 2 as a function of temperature P gas : partial pressure;  : absorption coefficient T   tilt toward the C 2 oxidative photosynthetic cycle

ROS

Photorespiration depends on the photosynthetic electron transport system

The biological function of photorespiration is under investigation ＊ a protective, to dissipate excess ATP and reducing power, especially under high light intensity and low [CO 2 ] 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

CO 2 -concentrating mechanisms: A. C 4 photosynthetic carbon fixation (C 4 ), in hot environment; B. Crassulacean acid metabolism (CAM), in desert environment; C. CO 2 pumps at the plasma membrane. In aquatic plants, such as unicellular cyanobacteria and algae. In aquatic environment, [CO 2 ] low  rubisco specificity activity low CO 2 -HCO 3 - pumps at the plasma membrane are induced, to accumulate inorganic carbon light energy provide ATP to uptake CO 2 and HCO 3 - carbonic anhydrase: HCO H + → H 2 O + CO 2 → Calvin cycle [CO 2 ] ↑  suppress photorespiration 0.03% CO 2 / 21% O 2

Cyanobacterial CO 2 concentrating mechanism — high homologous to the Rheus, a protein in erythrocytes

The C 4 carbon cycle Kranz (wreath) cells: present two distinct chloroplast-containing cells, mesophyll and bundle sheath cells spatial OAA

Calvin cycle

sugarcane Flaveria australasica Poa sp

The C 4 photosynthetic pathway: Hatch and Slack Gramineae (corn, millet, sorghum, sugarcane); Chenopodiaceae (Atriplex); Cyperaceae (sedges). external vascular NADP-ME: in chloroplast NAD-ME: in mitochondria PEP carboxykinase: in cytosol plasmodesmata specific translocators

Web Topic 8.7 (?) Three variations of C 4 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 C arbon a ssimilation r eduction

Borszczowia aralocaspica Bienertia cycloptera Chloroplasts containing rubisco are near mitochondria with NAD-ME