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Photosynthesis Innovations and Flaws: Discovering C3, C4, and CAM Pathways

Learn about the fatal flaws and innovative adaptations in photosynthesis, including C3, C4, and CAM pathways. Explore how plants overcome challenges to maximize CO2 intake and minimize water loss. Delve into the unique leaf anatomies and advantages of each pathway.

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Photosynthesis Innovations and Flaws: Discovering C3, C4, and CAM Pathways

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  1. Ch. 2 Photosynthesis (Ps) and Light

  2. Fatal Flaws of Fotosynthesis!

  3. Fatal Flaws of Fotosynthesis! • 1) Water loss/CO2 gain conundrum (=dilemma) • To gain C: open stomata, will lose water!

  4. Fatal Flaws of Fotosynthesis! • 2) Photorespiration: LOSS C (NOT C gain) • What drives?

  5. Fatal Flaws of Fotosynthesis! • 2) Photorespiration • Increases as: • 1) light intensity increases • 2) leaf temperature increases • 3) ratio O2:CO2increases • More CO2, lots Ps • Less CO2, less Ps

  6. C4 Photosynthesis • 3 patterns: • C3 Ps • C4 Ps • CAM Ps • Minimize FFF • C4 photosynthesis

  7. C4 leaf anatomy • Kranz anatomy (“wreath:” German) • Bundle sheath cells (BSC)

  8. C4 pathway • Mesophyll fix CO2 New enzyme (PEP carboxylase)

  9. C4 pathway • PEP carboxylase: 3 C (PEP) + CO2 = 4 C acid • Acid to BSC Why called C4 Ps?

  10. C4 pathway • BSC: Reaction reversed….CO2 + pyruvate (3 C) • CO2 to Calvin Cycle • Pyruvate to mesophyll, converted to PEP Calvin Cycle (Rubisco) C shuttle!!

  11. C4 pathway • C fixation & Ps separated

  12. C4 pathway • Advantages? FFF?

  13. C4 advantages • Benefits: • 1) PEP Carboxylase fix C • High affinity • No reaction Photorespiration: A FFF!

  14. C4 advantages • Benefits: • 2) CO2 concentrated bundle sheath • O2:CO2 low, low _________ • If photorespiration, CO2 ________

  15. A FFF! C4 advantages • Benefits: • 3) Less • PEP carboxylase hi affinity CO2“Sucks” CO2 well Stoma C4 Good sucker?

  16. C4 advantages • Benefits: • 4) Decrease Rubisco: more Ps w/ less N • High NUE (nitrogen use efficiency): biomass made per _______ Now: CAM

  17. CAM photosynthesis • CAM: Crassulacean Acid Metabolism • Crassulaceae: family succulents • Acid: Leaves acidic Diamorpha smallii (Crassulaceae)

  18. Leaf anatomy • Succulent (fleshy) leaves (or photosynthetic stems)

  19. Leaf anatomy • Succulent (fleshy) leaves (or photosynthetic stems) • Mesophyll not layered • Cells large: large vacuoles • Vascular bundle sheath _____

  20. CAM pathway • Separates C fixation & Ps in time rather than space! Separation in space: C4

  21. CAM pathway • Night: • Stomata _______ • CO2 fixed: PEP carboxylase makes 4 C acid Malic acid

  22. CAM pathway • Acid stored __________ • Leaf pH down @ night (“acid drop”) Acid drop in skateboarding

  23. CAM pathway • Day • Stomata close. • Reaction reversed • Ps: Calvin Cycle

  24. CAM pathway • Separates C fixation & Ps in time (not space!) Day Night

  25. CAM advantages • 1) PEP carboxylase fix C: photorespiration

  26. CAM advantages • 2) Stomata open night.

  27. CAM advantages • 3) Stomata close day. Seal CO2 in, low O2:CO2 ratio = low ____________

  28. CAM variation • Some: CAM when stressed (C3 other times) • CAM & succulence correlated (Fig. 2.14) Aeonium arboreum Fig. 2.14 More succulence, More CAM

  29. CAM • Carbon cycling: capture respiration CO2 night, ________ • Ex, Welwitschia mirabilis (Namib desert) • Gymnosperm Some plants may be 1,000 yr old

  30. Comparing C3, C4, CAM plants • Taxa: most plants (90%) • C4 plants: 3% flowering plants • Exs: • Some grasses: Sugar cane (Saccharum spp.)

  31. Amaizing Facts* • Corn or maize (Zea mays) *another corny Boyd joke.....

  32. Comparing C3, C4, CAM plants • Dicots: • Kudzu (Pueraria montana)

  33. Comparing C3, C4, CAM plants • Typical C4 habitat: • Temperate areas: • winter/spring ___ season • summer ___ season

  34. Comparing C3, C4, CAM plants • % grass flora C4 in N. America Fig. 2.18

  35. Comparing C3, C4, CAM plants • CAM: in 20 families flowering plants (7% all plants) • Exs: many cacti (saguaro, cholla) Saguaro “arms”

  36. Comparing C3, C4, CAM plants • CAM: in 20 families of flowering plants • Exs: Agave species • Economic use??

  37. Comparing C3, C4, CAM plants • Exs: some Crassulaceae (Diamorpha smallii)

  38. CAM and Epiphytes • Epiphytes: plants • Abundant tropical rain forests

  39. CAM and Epiphytes • Spanish moss (Tillandsia usneoides) • CAM plant: pineapple family (Bromeliaceae)

  40. Comparing C3, C4, CAM plants • Exs: many Orchidaceae (esp. epiphytic ones)

  41. Comparing C3, C4, CAM plants • CAM plants: • Succulents (deserts) • Epiphytes (tropical/subtropical areas)

  42. Comparing C3, C4, CAM plants • Trait C3 C4 CAM • Max. Ps rate Fig. 2.12

  43. Comparing C3, C4, CAM plants • Trait C3 C4 CAM • Optimum Ps temp. Fig. 2.11

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