Photorespiration and Plant Diversity

1
Photorespiration and Plant Diversity
2
On hot dry days

• Plants close stomata to prevent water loss
• This means less CO2 available for photosynthesis
• O2 builds up in mesophyll and competes with CO2
  for active site of rubisco

3

• Some intermediates of Calvin degraded into CO2
  and H20 photorespiration
• Occurs in presence of light
• Requires O2
• Results in CO2 and H20 (same as cellular
  respiration), but no ATP produced
• Photorespiration reduces photosynthetic
  efficiency

4
C4 and CAM plants have adaptations to reduce
photorespiration
5
Review of Leaf Cross-Sections
C4 Leaf
C3 Leaf
6
C4 Plants

• First fix CO2 into 4-C oxaloacetate
• Mesophyll cells
• Prior to Calvin Cycle
• Uses enzyme PEP carboxylase high affinity for
  CO2
• Oxaloacetate, through intermediates, delivers CO2
  to Calvin Cycle
• In bundle sheath cells
• Requires input of energy to recycle PEP

7
(No Transcript)
8
Pros Cons

• In high light areas, photorespiration is
  negliglible in C4 plants
• Photosynthetic yield is worth expenditure of 30
  ATPs
• In lower light/temperature, C3 plants are favored

9
CAM Plants

• Found in plants in xeric conditions
• Only open stomata at night
• Use PEP carboxylase to fix CO2
• During day, CO2 is removed from malate
• CO2 then enters Calvin

10
(No Transcript)
11
C4 vs. CAM plants

• Both use PEP carboxylase and form oxaloacetate
• In C4 plants C4 and C3 pathways occur in
  different locations
• In CAM plants, CAM and C3 pathways occur at
  different times