1. Jan. 25th, 2011 B4730/5730 Plant Physiological Ecology
Photosynthesis I

2. Use of Environmental Response Curves in Photosynthesis
Response curves help propose and test physiological mechanisms in ecology
Light response reveals some light dependent mechanisms
Parameters: quantum yield, saturation, compensation, curvature
CO2 responses reveals some light independent mechanisms
Parameters: supply, demand, compensation, Rubisco, RuBP, CO2 and Phosphate
Multivariate controls on response curves

3. C.m. shade C3, H.v. sun C3, Z.m. sun C4
BL blue light, RL red light
Bukhov et al 1995 J. Photo. Chem. Bio.

4. Pinus pinaster, Medlyn et al 2002 PCE

5. States of Calvin Cycle Photosynthesis
State one-Rubsico limited
CO2 low
No Vcmax limitation
State two-RuBP regeneration limited
Light limited
Enzymes of Calvin cycle limited
Increases with increasing CO2
State three-Triose Phosphate Use (TPU)
Photosynthesis at higher rate than capacity to use products
Not CO2 or O2 limited
Actual A rate is which of three states is limiting
Farqhuar et al (1980) model used to determine which one

6. Sharkey et al. PCE 2007; incorporates newest material to Farquhar model

7. Farquhar Model Overview
Five parameters from Farquhar model
VCmax - maximum carboxylation by Rubisco
J - rate of photosynthetic electron transport
TPU - triose phosphate use
Rd - day respiration
gm-mesophyll conductance
Parameters adjusted to 25 °C for comparison
c is scaling constant = 1 at 25 C), ΔHa enthalpy of activation, ΔHd enthalpy of deactivation, ΔS entropy, R is universal gas constant, T is temperature in K

8. Sharkey et al. 2007

9. Rubisco limited Farquhar Model
Vcmax maximum Rubsico carboxylation
Cc CO2 partial pressure at Rubisco site
Kc Michaelis constant for CO2
O partial pressure O2
Ko Michaelis constant for oxygenation
Γ* [CO2] at which photosynthetic CO2 uptake compensated by photorespiration
Rd mitochondrial respiration

10. RuBP Regen and TPU Farquhar Model
J rate of electron transport
4 electrons per oxygenation and carboxylation
A=3TPU-Rd
TPU rate of use of triose phosphates for any export of C from Calvin cycle, includes photorespiratory use of glycine and serine

11. Mimimimum of three limitation
gives actual A and J rates.
Farquhar et al. Planta 1980;
Long and Bernacchi J Ex Bot. 2003

12. Ethier et al PCE 2006,
Pseudotsuga menziesii needle ages

13. Filled crop, open broadleaf, crosses conifers
Medlyn et al. PCE 2002

14. Light Dependent Reactions
Three fates of photon striking reaction center
Heat, fluorescence, photochemistry
Linear electron flux (LEF) goes from PSII to PSI to drive H+ pmf,
Cyclic flux around PSI
Low light, efficiency maximized
High light, energy dissipation maximized
redox, xanthophyll cycle, photorespiration

15. Baker et al. PCE 2007