Topics:

1.CO2 concentrating mechanisms2.Starch and Sucrose synthesis

RuBis Carboxylase/Oxygenase

The cost of photorespiration

3x O2 needs 2x ATP and 2x Ferredoxin

AND high temperature increases photorespiration:*Modifies Rubisco’s kinetics: oxygenation more favorable*Decreases the CO2/O2 ratio in solution

Why do they do this?

What do plants do?

CO2 Concentrating Mechanisms

a) CO2 and HCO3- Pumps

b) C4 Photosynthesisc) Crassulacean Acid Metabolism (CAM)

(Tanaka et al., 2008; Yeates Lab, UCLA)Nevo et al., 2007

Carboxysomes: Rubisco, Carbonic anhydrase

CO2 and HCO3- Pumps: Aquatic Organisms

Cyanobacteria Thylakoid

CO2 Concentrating Mechanisms

a) CO2 and HCO3- Pumps

b) C4 Photosynthesisc) Crassulacean Acid Metabolism (CAM)

PEP-Carboxylase

CH2

IIC-OPO3

2- + HCO3-

ICOO-

COO-

ICH2 + HPO4

2-

IC=O ICOO-

Could plants just use PEP-carboxylase instead of Rubisco?

C3 + HCO3-

C4

C3 + CO2

HCO3- CO2

RUBISCO

C3

Fixation/carboxylation

C4 transport

Decarboxylation

C3-”recycling”

The C4 carbon cycle: Spatial separation

a. Different Cells: Bundle Sheath cells/ Kranz anatomyb. Within one cell

Kranz Anatomy

Bundle sheath cells

The C4 carbon cycle: Spatial separation

Unstacked thylakoids (PSI)

Starch

Stacked thylakoids (PSI+PSII)

No starch

CHLOROPLASTS

The C4 carbon cycle: Modifications

Convergent evolution

(V

Single Cell C4 Photosynthesis

Borszczowia

Bienertia

Voznesenskaya et al., 2002

CO2 Concentrating Mechanisms

a) CO2 and HCO3- Pumps

b) C4 Photosynthesisc) Crassulacean Acid Metabolism (CAM)

PEP-Carboxylase

CH2

IIC-OPO3

2- + HCO3-

ICOO-

COO-

ICH2 + HPO4

2-

IC=O ICOO-

CAM: temporal separationMinimizing water loss

H20 loss/CO2 gained (g)CAM 50-100gC4 250-300gC3 400-500

CAM: Day/Night switch

CO2 Concentrating Mechanisms

a) CO2 and HCO3- Pumps

b) C4 Photosynthesisc) Crassulacean Acid Metabolism (CAM)

PEP-Carboxylase

CH2

IIC-OPO3

2- + HCO3-

ICOO-

COO-

ICH2 + HPO4

2-

IC=O ICOO-

PEPC regulationC4

PEPCPEPC PEPCPEPC PP

PEPC-KinasePEPC-Kinase

ATP ADP

PP

PEPC-KinasePEPC-Kinase

PEPCPEPC PEPCPEPC PP

PEPC-KinasePEPC-Kinase

ATP ADP

PP

MetabolitesSalt stressCircadian clock

CAM

Topics:

1.CO2 concentrating mechanisms2.Starch and Sucrose synthesis

Triose-P Glc-1-P Glc-NtDP

NTP(ATP/UTP)

PPi

Saccharides

Saccharide Synthesis: Overview

Pi

Plastids: Starch Synthesis

Remember: Cellulose = -D-1,4-glucosyl

Starch is a branched polymer

PHOSPHOROLYTIC HYDROLYTIC

Triose-P Glc-1-P Glc-NtDP

NTP(ATP/UTP)

PPi

Saccharides

Saccharide Synthesis: Overview

Pi

Triose-P

Fru-1,6-bisP

Fru-6-P

Glc-6-P

Glc-1-P

UDP-Glc

Suc-6-P

PiPi

PPi

ATP

ADP

PPi

UTP

PiSucrose

SPS

Regulation of Starch and Sucrose Synthesis

Pi

Fru-1,6-bisP

Fru-6-PFru-2,6-bisP

Fru-1,6-bisP-Phosphatase

UDP-Glc + Fru-6-P Suc-6P

Sucrose-P Synthase (SPS)

Glc-6-P

SPS-P

SPS

Pi

Glc-1-P

ADP-Glc

ATP

PPi2xPi

Pi

3PGAFerredoxinRed.

ADP-Glc Pyrophosphorylase (AGPase)

Cytosol Plastid

Triose-PTriose-P

Pi Pi

Sucrose Synthesis

Starch Synthesis

Balance: Starch vs Sucrose Synthesis