Ch. 2 Photosynthesis (Ps) and Light

C4 Photosynthesis• 3 patterns:

– C3 Ps

– C4 Ps

– CAM Ps

• Minimize FFF (fatal flaws of fotosynthesis)

C4 photosynthesis

C4 leaf anatomy• Kranz anatomy (“wreath:” German):

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

C4 pathway• PEP carboxylase:

Why calledC4 Ps?

C4 pathway• BSC: Reaction reversed….• CO2 to• Pyruvate to

C shuttle!!

Calvin Cycle (Rubisco)

C4 pathway• C fixation & Ps

C4 pathway

• Advantages?

FFF?

Fatal Flaws of Fotosynthesis!

C4 advantages• Benefits:

– 1) PEP Carboxylase fix C

Photorespiration: A FFF!

C4 advantages• Benefits:

– 2) CO2 concentrated bundle sheath

C4 advantages• Benefits:

– 3) Less H20 loss.

Stoma

C4

Good sucker?

A FFF!

C4 advantages• Benefits:

– 4) Decrease Rubisco:– High NUE (nitrogen use efficiency):

Now:CAM

CAM photosynthesis• CAM:• Crassulaceae: • Acid: Leaves

Diamorpha smallii(Crassulaceae)

Leaf anatomy• Succulent

Leaf anatomy• Mesophyll• Cells large: • Vascular bundle sheath

CAM pathway• Separates C fixation & Ps

Separation in space: C4

CAM pathway• Night:

– Stomata open

– CO2 fixed:

Malic acid

CAM pathway• Acid stored• Leaf pH

Acid drop inskateboarding

CAM pathway• Day

– Stomata

– Reaction

– Ps: Calvin Cycle

CAM pathway• Separates C fixation and Ps

Night Day

CAM advantages• 1) PEP carboxylase fixes C:

photorespiration

CAM advantages• 2) Stomata open night. Less water loss!

CAM advantages• 3) Stomata closed day.

CAM variation• Dependence on CAM varies• Some: • CAM & succulence

Fig. 2.14More succulence,More CAM

Aeonium arboreum

CAM variation• Carbon cycling:

• Ex, Welwitschia mirabilis (Namib desert S. Africa)

• Gymnosperm: 2 leaves!

Some plants may be 1,000 yr old

Comparing C3, C4, CAM plants• Taxa: most plants

• C4 plants:

• Exs:• Some grasses: Sugar cane (Saccharum spp.)

Amaizing Facts*• Corn or maize (Zea mays)

*another cornyBoyd joke.....

Comparing C3, C4, CAM plants• Dicots:

– Kudzu (Pueraria montana)

Comparing C3, C4, CAM plants• Typical C4 plant habitat:

• In temperate areas: – winter/spring

– summer

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

Fig. 2.18

Comparing C3, C4, CAM plants• CAM plants:

• Exs: many cacti (saguaro, cholla)

Saguaro “arms”

Comparing C3, C4, CAM plants• Exs: Agave species

– Economic use??

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

CAM and Epiphytes• Epiphytes:

– Abundant tropical rain forests

CAM and Epiphytes• Alabama• Spanish moss (Tillandsia

usneoides)• CAM plant:

Comparing C3, C4, CAM plants• Exs: many

(esp. epiphytic ones)

Comparing C3, C4, CAM plants• CAM plants:

Comparing C3, C4, CAM plants• Trait C3 C4 CAM

• Max. Ps rate

Fig. 2.12

Comparing C3, C4, CAM plants• Trait C3 C4 CAM

• Max. growth rate• (optimal conditions)

Comparing C3, C4, CAM plants• Trait C3 C4 CAM

• Optimum Ps temperature

Fig. 2.11