topics: 1.co2 concentrating mechanisms 2.starch and sucrose synthesis
TRANSCRIPT
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