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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