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Ch. 2 Photosynthesis (Ps) and Light Fatal Flaws of Fotosynthesis! Fatal Flaws of Fotosynthesis! • 1) Water loss/CO2 gain conundrum (=dilemma) • To gain C: open stomata, will lose water! Fatal Flaws of Fotosynthesis! • 2) Photorespiration: LOSS C (NOT C gain) • What drives? Fatal Flaws of Fotosynthesis! • 2) Photorespiration • Increases as: – 1) light intensity increases – 2) leaf temperature increases – 3) ratio O2:CO2 increases • More CO2, lots Ps • Less CO2, less Ps C4 Photosynthesis • 3 patterns: – C3 Ps – C4 Ps – CAM Ps • Minimize FFF C4 photosynthesis C4 leaf anatomy • Kranz anatomy (“wreath:” German) • Bundle sheath cells (BSC) C4 pathway • Mesophyll fix CO2 New enzyme (PEP carboxylase) C4 pathway • PEP carboxylase: 3 C (PEP) + CO2 = 4 C acid • Acid to BSC Why called C4 Ps? C4 pathway • BSC: Reaction reversed….CO2 + pyruvate (3 C) • CO2 to Calvin Cycle • Pyruvate to mesophyll, converted to PEP Calvin Cycle (Rubisco) C shuttle!! C4 pathway • C fixation & Ps separated C4 pathway • Advantages? FFF? • Benefits: C4 advantages – 1) PEP Carboxylase fix C – High affinity – No reaction Photorespiration: A FFF! • Benefits: C4 advantages – 2) CO2 concentrated bundle sheath – O2:CO2 low, low _________ – If photorespiration, CO2 ________ C4 advantages A FFF! • Benefits: – 3) Less – PEP carboxylase hi affinity CO2 “Sucks” CO2 well Stoma C4 Good sucker? • Benefits: C4 advantages – 4) Decrease Rubisco: more Ps w/ less N – High NUE (nitrogen use efficiency): biomass made per _______ Now: CAM CAM photosynthesis • CAM: Crassulacean Acid Metabolism • Crassulaceae: family succulents • Acid: Leaves acidic Diamorpha smallii (Crassulaceae) Leaf anatomy • Succulent (fleshy) leaves (or photosynthetic stems) Leaf anatomy • • • • Succulent (fleshy) leaves (or photosynthetic stems) Mesophyll not layered Cells large: large vacuoles Vascular bundle sheath _____ CAM pathway • Separates C fixation & Ps in time rather than space! Separation in space: C4 • Night: CAM pathway – Stomata _______ – CO2 fixed: PEP carboxylase makes 4 C acid Malic acid CAM pathway • Acid stored __________ • Leaf pH down @ night (“acid drop”) Acid drop in skateboarding • Day CAM pathway – Stomata close. – Reaction reversed • Ps: Calvin Cycle CAM pathway • Separates C fixation & Ps in time (not space!) Night Day CAM advantages • 1) PEP carboxylase fix C: photorespiration CAM advantages • 2) Stomata open night. CAM advantages • 3) Stomata close day. Seal CO2 in, low O2:CO2 ratio = low ____________ CAM variation • Some: CAM when stressed (C3 other times) • CAM & succulence correlated (Fig. 2.14) Aeonium arboreum Fig. 2.14 More succulence, More CAM CAM • Carbon cycling: capture respiration CO2 night, ________ • Ex, Welwitschia mirabilis (Namib desert) • Gymnosperm Some plants may be 1,000 yr old Comparing C3, C4, CAM plants • • • • Taxa: most plants (90%) C4 plants: 3% flowering plants Exs: Some grasses: Sugar cane (Saccharum spp.) Amaizing Facts* • Corn or maize (Zea mays) *another corny Boyd joke..... Comparing C3, C4, CAM plants • Dicots: – Kudzu (Pueraria montana) Comparing C3, C4, CAM plants • Typical C4 habitat: • Temperate areas: – winter/spring ___ season – summer ___ season Comparing C3, C4, CAM plants • % grass flora C4 in N. America Fig. 2.18 Comparing C3, C4, CAM plants • CAM: in 20 families flowering plants (7% all plants) • Exs: many cacti (saguaro, cholla) Saguaro “arms” Comparing C3, C4, CAM plants • CAM: in 20 families of flowering plants • Exs: Agave species – Economic use?? Comparing C3, C4, CAM plants • Exs: some Crassulaceae (Diamorpha smallii) CAM and Epiphytes • Epiphytes: plants – Abundant tropical rain forests CAM and Epiphytes • Spanish moss (Tillandsia usneoides) • CAM plant: pineapple family (Bromeliaceae) Comparing C3, C4, CAM plants • Exs: many Orchidaceae (esp. epiphytic ones) Comparing C3, C4, CAM plants • CAM plants: – Succulents (deserts) – Epiphytes (tropical/subtropical areas) Comparing C3, C4, CAM plants • Trait • Max. Ps rate C3 C4 CAM Fig. 2.12 Comparing C3, C4, CAM plants • Trait • Optimum Ps temp. C3 C4 CAM Fig. 2.11