1. Plant Physiology 2- Photosynthesis

2. photosynthesis Photo means ‘light’ and synthesis means ‘to make’
Process in which plants convert carbon dioxide and water into sugars using solar energy
Occurs in chloroplast

3. photosynthetic products often stored as starch
Photosynthesis:
6 CO H2O C6 H12 O O2
carbon dioxide water = sugar + oxygen
photosynthetic products often stored as starch
Starch = glucose polymer
features same as in Chlorophyta (green algae)
3. similar photosynthetic storage product: starch
aerobic photosynthesis more efficient than anaerobic
Fig Photosynthesis
STARCH
Tracking atoms

5. Fig. 10.1

6. Fig. 10.2a

7. Fig. 10.2b

8. Fig. 10.2c

10. Fig. 10.4

11. Chlorophyll
Absorbs red & blue light
Reflects green light

12. Fig. 10.6

13. Fig. 10.8

17. Fig

18. Fig

19. Rubisco Ribulose bisphosphate carboxylase oxygenase (fixes CO2 & O2)
Enzyme in Calvin Cycle (1st step)
Most abundant protein on Earth
Ca. 25% total leaf protein

20. Photorespiration When rubisco “fixes” O2, not CO2
Lose 1/2 C as CO2; costs 2.5 extra ATP
Take up O2
Only occurs in light
Occurs 1 out of 4 reactions under today’s atmospheric [CO2]
Rate increases with temperature

23. Types of photosynthesisC3
The majority of plants C4
CO2 temporarily stored as 4-C organic acids resulting in more more efficient C exchange rate
Advantage in high light, high temperature, low CO2
Many grasses and crops (e.g., corn, sorghum, millet, sugar cane)
CAM
Stomata open during night
Advantage in arid climates
Many succulents (e.g., cacti, euphorbs, bromeliades, agaves)

24. Fig

26. Fig

27. Global Environmental Change & Photosynthesis: C3 vs. C4 vs. CAM
Increasing CO2
Increasing chronic and acute temperatures
Increasing N (vs. decreasing C:N from increasing CO2)
Changes in water

31. CO2 effects on photosynthesis
C4 > C3 at low CO2
But, C3 > C4 at high CO2

32. *At high CO2, C3 more efficient than C4 at all temps.
(photosynthesis only, not other processes)

33. Photosynthetic N-use efficiency
C4 plants need (have) less leaf N than C3
Photosynthesis higher per unit N in C4
Humans are increasing global N, which benefits C3 more than C4
Increasing CO2 decreases leaf N content, more in C3 than C4

34. Photosynthetic water-use efficiency
C4 plants use less water than C3
(cause stomates open less)
Water availability may increase or decrease in the future.

35. Predicting the future for plants
How will increases in CO2, N, and chronic and acute heat stress affect photosynthesis?
Who will win or lose? C3? C4?
How will pollution (eg, ozone) interact?
Current research in my lab an example.

37. Hypothesis High CO2 effects greater in C3 than C4 and CAM species.
Elevated CO2
High CO2 effects greater in C3 than C4 and CAM species.
High CO2 effects greater on induced than basal thermotolerance.
Increased leaf C:N
Decreased
thermotolerance
Decreased Heat-shock proteins (Hsps)

38. Heat stress decreased Pn in all species
(not the result of stomatal closure).
Elevated CO2 had negative effects on Pn of C4 species, and positive effects on C3 species.
Pre-heat shock has a positive effect on Pn.

39. Heat shock decreased Фet of all C3 and C4 species
There was negative CO2 effects on all species, except for wheat
There was positive Pre-HS effects on all species

40. SoyFACE: CO2 & ozone