Chapter 10Plant metabolism -

photosynthesis

Photosynthesis Photosynthesis is an

anabolic process that combines carbon dioxide and water in the presence of light with the aid of chlorophyll and transforms the energy from the sun to biochemical energy in the bonds between the atoms in a sugar molecule; oxygen is a by-product.

Photosynthesis Photosynthesis is an

anabolic process that combines carbon dioxide and water in the presence of light with the aid of chlorophyll and transforms the energy from the sun to biochemical energy in the bonds between the atoms in a sugar molecule; oxygen is a by-product.

C-source

Global warming

Photosynthesis Photosynthesis is an

anabolic process that combines carbon dioxide and water in the presence of light with the aid of chlorophyll and transforms the energy from the sun to biochemical energy in the bonds between the atoms in a sugar molecule; oxygen is a by-product.

Isotope

Sole source of O2

Photosynthesis Photosynthesis is an

anabolic process that combines carbon dioxide and water in the presence of light with the aid of chlorophyll and transforms the energy from the sun to biochemical energy in the bonds between the atoms in a sugar molecule; oxygen is a by-product.

P680P700

Photosynthesis Photosynthesis is an

anabolic process that combines carbon dioxide and water in the presence of light with the aid of chlorophyll and transforms the energy from the sun to biochemical energy in the bonds between the atoms in a sugar molecule; oxygen is a by-product.

Photosynthesis … transforms the energy from

the sun to biochemical energy in the bonds between the atoms in a sugar molecule; oxygen is a by-product.

ADPNADP

ATPNADPH

Elec

tron

flow

(Z s

chem

e)

H2O

O2

Calvin cycle

CO2 RuBP

Light-dependent reaction

Light-independent reactionCarbon-fixing and reducing reaction

Photosynthesis Water molecules are split, releasing e-, H+, and O2

e- passing along electron transport system H+ is involved in NADP to form NADPH ATP molecules are produced

ADPNADP

ATPNADPH

Z sc

hem

e

H2O

O2

Light-dependent reaction

Photosynthesis

Water molecules are split, releasing e-, H+, and O2

Light-dependent reaction

Photosynthesis

Water molecules are split, releasing e-, H+, and O2

Electron flow: e- passing along electron transport

system

Light-dependent reaction

Z scheme

Photosynthesis

Water molecules are split, releasing e-, H+, and O2

e- passing along electron transport system H+ is involved in NADP to form NADPH

Light-dependent reaction

Photosynthesis

Water molecules are split, releasing e-, H+, and O2

e- passing along electron transport system H+ is involved in NADP to form NADPH ATP molecules are produced

Light-dependent reaction

Photophosphorylation

Photosynthesis … transforms the energy from

the sun to biochemical energy in the bonds between the atoms in a sugar molecule; oxygen is a by-product.

ADPNADP

ATPNADPH

Elec

tron

flow

(Z s

chem

e)

H2O

O2

Calvin cycle

CO2 RuBP

Light-dependent reaction

Light-independent reactionCarbon-fixing and reducing reaction

Photosynthesis

Water

Light-independent reaction

Calvin cycle

Photosynthesis

Carboxylation

Light-independent reaction

Calvin cycle

6 CO2 + 6 RuBPRubisco(RuBP carboylase/oxygenase)

12 3PGA

Photosynthesis

Carboxylation Reduction

Light-independent reaction

Calvin cycle

6 CO2 + 6 RuBPRubisco(RuBP carboylase/oxygenase)

12 3PGA

12 GA3P

Photosynthesis

Carboxylation Reduction Regeneration

Light-independent reaction

Calvin cycle

6 CO2 + 6 RuBPRubisco(RuBP carboylase/oxygenase)

12 3PGA

10 GA3P

6 RuBP

2 GA3P+

Photosynthesis

Photosynthesis vs. photorepiration Stomata are closed under hot and dry climates, which

leads to a decreased CO2:O2 ratio and hence promote photorespiration

How to inhibit photorespiration and hence promote fixation of CO2

ADPNADP

ATPNADPH

Elec

tron

flow

(Z s

chem

e)

H2O

O2

Calvin cycle

CO2 RuBP

Photo-respiration

Photosynthesis vs. photorepiration

How to inhibit photorespiration and hence promote fixation of CO2

Calvin cycle

CO2 RuBP

Photo-respiration

Photosynthesis vs. photorepiration

Increasing CO2:O2 ratio

CO2 are combined with PEP (a 3-carbon compound), producing OAA (a 4-carbon compound) in mesophyll cells

The 4-carbon compounds are transported to the bundle sheath cells where CO2 are released, concentrated and enter the Calvin cycle.

Photosynthesis: the 4-Carbon pathway

Mesophyll cells: CO2 + PEP → OAA Bundle sheath cells: 4-C → CO2 → Calvin cycle.

Photosynthesis: the 4-Carbon pathway

Kranz anatomy leave

How to inhibit – C4 photosynthesis

ADPNADP

ATPNADPH

Elec

tron

flow

(Z s

chem

e)

H2O

O2

Calvin cycle

CO2 RuBP

Photo-respiration

Photosynthesis vs. photorepiration

Mesophyll cell

- OAA

BSC – concentrated

CO2

Night: CO2 + PEP → OAA → malic acidaccumulating organic acids in vacuole

Day: 4-C → CO2 → Calvin cyclereleasing CO2 in mesophyll cell

Photosynthesis: CAM pathway

ADPNADP

ATPNADPH

Elec

tron

flow

(Z s

chem

e)

H2O

O2

Calvin cycle

CO2 RuBP

Photo-respiration

Photosynthesis

Mesophyll cell

- OAA

BSC – concentrated

CO2

Night – accumulating organic acids in vacuole

Day – concentrated CO2 in mesophyll cell

C3 plantC4 plantCAM plant