Processes affected by pCO 2 Pathways that use CO 2 as substrate

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)

Processes affected by pCO2

Calvin cycle (Carbon reduction pathway)1)RuBP binds CO2 2) rapidly splits into two 3-Phosphoglycerate

• therefore called C3 photosynthesis

Processes affected by pCO2

Calvin cycle (Carbon reduction pathway)1)RuBP binds CO2 2) rapidly splits into two 3-Phosphoglycerate3) catalyzed by Rubisco (ribulose 1,5 bisphosphate carboxylase/oxygenase)the most important & abundant protein on earth

•Lousy Km

•Rotten Vmax!

Processes affected by pCO2

Calvin cycle (Carbon reduction pathway)Reversing glycolysisconverts 3-Phosphoglycerate to G3Pconsumes 12 ATP & 12 NADPH/glucose

Processes affected by pCO2

Calvin cycle (Carbon reduction pathway)Reversing glycolysisG3P has 2 possible fates

1) 1 in 6 becomes (CH2O)n

2) 5 in 6 regenerate RuBP

Processes affected by pCO2

5 in 6 G3P regenerate RuBPBasic problem: converting a 3C to a 5C compoundfeed in five 3C sugars, recover three 5C sugars

Regenerating RuBPBasic problem: converting a 3C to a 5C compoundmust assemble intermediates that can be broken into 5 C sugars after adding 3C subunit

Processes affected by pCO2

1)Pathways that use CO2 as substrate•Calvin cycle (Carbon reduction pathway)• Rubisco must be carbamylated & bind Mg2+ to be active!

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)• Rubisco must be carbamylated & bind Mg2+ to be active!• RuBP binds & inactivates uncarbamylated rubisco

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)• Rubisco must be carbamylated & bind Mg2+ to be active!• RuBP binds & inactivates uncarbamylated rubisco• Rubisco activase removes this RuBP (also CA1P)

Processes affected by pCO2

rubisco usually limits C3 -> limited by demand for CO2

Supply is limited by resistance to CO2 diffusion• Boundary layer• Stomatal: only one that can be adjusted• Liquid phase

Processes affected by pCO2

rubisco usually limits C3 -> limited by demand for CO2

Supply is limited by resistance to CO2 diffusion• Boundary layer• Stomatal: only one that can be adjusted• Liquid phase

Demand is set by mesophyll,Stomata control supply

Processes affected by pCO2

Demand is set by mesophyll, stomata control supplyCi is usually much lower than Ca

A vs Ci plots tattle on the Calvin cycle

Processes affected by pCO2

A vs Ci plots tattle on the Calvin cycle • In linear phase rubisco is limiting• When curves RuBP or Pi regeneration is limiting

Processes affected by pCO2

Currently Rubisco usually limits C3 plantsWill increase plant growth until hit new limiting factor

Processes affected by pCO2

Currently Rubisco usually limits C3 plantsWill increase plant growth until hit new limiting factor Free-Air CO2 Enrichment Experiments show initial gains,

but taper off w/in a few yearsNow are limited by nutrients or water

Processes affected by pCO2

Pathways that use CO2 as substrate•Calvin cycle (Carbon reduction pathway)•Carbonic anhydrase: used to increase Cp CO2

Processes affected by pCO2

Pathways that use CO2 as substrate•Calvin cycle (Carbon reduction pathway)•Carbonic anhydrase: used to increase Cp CO2

•First step in C4 photosynthesis: PEPcase fixes HCO3-

•also serves as CO2 sensor (mech unknown)

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)• Fatty acid synthesis

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)• Fatty acid synthesis• Phosphoenolpyruvate carboxylase

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)• Fatty acid synthesis• Phosphoenolpyruvate carboxylase: plants often

form malate cf pyr from glycolysis• Get more ATP/NADH

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Calvin cycle • Fatty acid synthesis• Phosphoenolpyruvate

carboxylase: plants often form malate cf pyr from glycolysis• Get more ATP/NADH• lets cells replace Krebs intermediates used for synthesis• First step in C4

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Calvin cycle (Carbon reduction pathway)• Fatty acid synthesis• PEP carboxylase• Pyruvate carboxylase (&/or malic enzyme)• gluconeogenesis

Processes affected by pCO2

1)Pathways that use CO2 as substrate• Pyruvate carboxylase • PEPcarboxykinase• carbamoyl phosphate synthetase: pyrimidine synthesis & ornithine/urea cycle

Processes affected by pCO2

1)Pathways that use CO2 as substrate2) Pathways that release CO2

• photorespiration: glycine decarboxylase

Processes affected by pCO2

1)Pathways that use CO2 as substrate2) Pathways that release CO2

• photorespiration: glycine decarboxylase• Respiration (+ malic enzyme)

Processes affected by pCO2

1)Pathways that use CO2 as substrate2) Pathways that release CO2

• Photorespiration• Respiration (+ malic enzyme)• CO2 Inhibits respiration at 3%• No obvious effects at 700 ppm, yet biomass reduced

pathways that release CO2• Photorespiration• Respiration • Pentose phosphate shunt in cytosol or cp

pathways that release CO2• Photorespiration• Respiration • Pentose phosphate shunt in cytosol or cp• Pyruvate decarboxylase in fermentation

Pathways that release CO2• Serine or Phosphatidylserine decarboxylase for

ethanolamine, choline, etc synthesis

Pathways that release CO2• Serine or Phosphatidylserine decarboxylase for ethanolamine, choline, etc synthesis• Aromatic Acid Decarboxylase for many precursors

Pathways that release CO2• Serine or Phosphatidylserine decarboxylase for ethanolamine, choline, etc synthesis• Aromatic Acid Decarboxylase for many precursors• Many more AA Decarboxylases

Processes affected by CO2

2) pathways that release CO2

3) transpiration & stomatal number