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Topics: CO2 concentrating mechanisms Starch and Sucrose synthesis

Topics: CO2 concentrating mechanisms Starch and Sucrose synthesis. RuBis Carboxylase/Oxygenase. The cost of photorespiration. Why do they do this?. 3x O 2 needs 2x ATP and 2x Ferredoxin. AND high temperature increases photorespiration:

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Topics: CO2 concentrating mechanisms Starch and Sucrose synthesis

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  1. Topics: • CO2 concentrating mechanisms • Starch and Sucrose synthesis

  2. RuBis Carboxylase/Oxygenase

  3. The cost of photorespiration Why do they do this? 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

  4. What do plants do?

  5. CO2 Concentrating Mechanisms • CO2 and HCO3- Pumps • C4 Photosynthesis • Crassulacean Acid Metabolism (CAM)

  6. CO2 and HCO3- Pumps: Aquatic Organisms Cyanobacteria Thylakoid Carboxysomes: Rubisco, Carbonic anhydrase Nevo et al., 2007 (Tanaka et al., 2008; Yeates Lab, UCLA)

  7. CO2 Concentrating Mechanisms • CO2 and HCO3- Pumps • C4 Photosynthesis • Crassulacean Acid Metabolism (CAM) PEP-Carboxylase CH2 II C-OPO32- + HCO3- I COO- COO- I CH2 + HPO42- I C=O I COO-

  8. Could plants just use PEP-carboxylase instead of Rubisco?

  9. HCO3- CO2 Fixation/carboxylation C3 + HCO3- C3-”recycling” C3 C4 C4 transport C3 + CO2 Decarboxylation RUBISCO

  10. The C4 carbon cycle: Spatial separation • Different Cells: Bundle Sheath cells/ Kranz anatomy • Within one cell

  11. Kranz Anatomy Bundle sheath cells

  12. The C4 carbon cycle: Spatial separation CHLOROPLASTS Stacked thylakoids (PSI+PSII) No starch Unstacked thylakoids (PSI) Starch

  13. The C4 carbon cycle: Modifications Convergent evolution

  14. (V Single Cell C4 Photosynthesis Voznesenskaya et al., 2002 Bienertia Borszczowia

  15. CO2 Concentrating Mechanisms • CO2 and HCO3- Pumps • C4 Photosynthesis • Crassulacean Acid Metabolism (CAM) PEP-Carboxylase CH2 II C-OPO32- + HCO3- I COO- COO- I CH2 + HPO42- I C=O I COO-

  16. CAM: temporal separation Minimizing water loss H20 loss/CO2 gained (g) CAM 50-100g C4 250-300g C3 400-500

  17. CAM: Day/Night switch

  18. CO2 Concentrating Mechanisms • CO2 and HCO3- Pumps • C4 Photosynthesis • Crassulacean Acid Metabolism (CAM) PEP-Carboxylase CH2 II C-OPO32- + HCO3- I COO- COO- I CH2 + HPO42- I C=O I COO-

  19. PEPC regulation CAM C4 Metabolites Salt stress Circadian clock PEPC-Kinase ATP ADP ATP ADP PEPC-Kinase PEPC-Kinase PEPC PEPC PEPC PEPC P P P P

  20. Topics: • CO2 concentrating mechanisms • Starch and Sucrose synthesis

  21. Saccharide Synthesis: Overview Saccharides Pi Triose-P Glc-1-P Glc-NtDP NTP (ATP/UTP) PPi

  22. Plastids: Starch Synthesis

  23. Starch is a branched polymer Remember: Cellulose = b-D-1,4-glucosyl

  24. PHOSPHOROLYTIC HYDROLYTIC

  25. Saccharide Synthesis: Overview Saccharides Pi Triose-P Glc-1-P Glc-NtDP NTP (ATP/UTP) PPi

  26. Pi Sucrose Suc-6-P UDP-Glc PPi UTP SPS Glc-1-P Glc-6-P Fru-6-P ATP Pi Pi PPi ADP Fru-1,6-bisP Triose-P

  27. Regulation of Starch and Sucrose Synthesis UDP-Glc + Fru-6-P Suc-6P SPS Glc-6-P Pi SPS-P Glc-1-P Pi ATP Sucrose-P Synthase (SPS) 3PGA 2xPi PPi Ferredoxin Red. Fru-2,6-bisP Fru-6-P ADP-Glc Pi ADP-Glc Pyrophosphorylase (AGPase) Fru-1,6-bisP Fru-1,6-bisP-Phosphatase

  28. Balance: Starch vs Sucrose Synthesis Plastid Cytosol Sucrose Synthesis Triose-P Triose-P Pi Pi Starch Synthesis

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