Last Time

1. Last Time Modeling Photosynthesis Farquhar & von Caemmerer Equations Physiological and Environmental Controls Stomate control Water stress and the A/Ci Curve

2. Today Anatomical regulation of photosynthesis Light Acclimation - Sun vs. Shade leaves Temperature responses of photosynthesis and thermal acclimation Photosynthetic pathway variation C3, C4, CAM

3. Acclimation vs. Acclimatization The physiological change of an organism to changes in climate or environment. Acclimate - Short-term physiological and behavioral adjustments Acclimatize (Acclimatization) - Longer term physiological change over a year. Often extensive physiological changes in tolerances. Both occur in within the lifetime of an organism Compare to Adaptation

4. Carbon and Water Flux Modeled by Stomatal Conductance Resistance = 1 / conductance 1/conductance = g Photosynthetic flux A ~ JCO2 = (Ci-Ca) / ∑ ri = gCO2(Ci - Ca) Water flux (transpiration) E ~ JH2O = (ei-ea)/ ∑ r = gH2O(ei - ea) where e = vapor partial pressures in the leaf or air (recall, its’ the hydrated surface within the intercellular airspace that is the site of evaporation…thus, temperature dependent)

5. Anatomical Regulation of C3 Photosynthesisvia modification of pathway resistance Three Primary Factors • Cell Size: • Changes in cell surface area and resistance of CO2 diffusion • Mesophyll Thickness: • Changes in cell surface area • Changes in chloroplast volume • Molecular distance of transport • Percent Air Space: • Changes in cell surface area • Changes in chloroplast volume • Changes in tissue blockage of CO2 molecules

6. Mesophyll Thickness Cell Size % air space + - + - + - - Cell surface area per unit leaf area Volume of chlorophyllous tissue per unit leaf area Molecular travel distances Tissue blockage of CO2 molecules + - - + Transport Resistance Enzyme Resistance Intercellular airspace resistance - - - Photosynthetic rate Photosynthetic rate Maximize photosynthesis - minimize resistances

7. How Can Plant Anatomy Influence A and E? Let’s Compare The Resistances of Three Leaves

8. Maximize photosynthesis Compromise Low resistance but thicker leaf (increased diffusion times, lower photosythesis per unit volume) Selection has acted to maximize Chlorophyll per unit volume and minimize resistance High chlorophyll per unit volume but high resistance Resistance Diffusion speed Photosynthesis

9. Influence of Light Environment on Photosynthesis Light Acclimatization and Adaptations

10. What is changing in these plants in terms of allocation? physiology?

11. Group Project You now know most of the basics of what limits photosynthesis Depending on the environment photosynthesis is limited by potentially many factors… Let’s think about leaves growing in a sunny environment and leaves growing in a shady environment What will natural selection operate on? How will they differ in terms of leaf anatomy, biochemistry, and gas exchange?

12. List of leaf traits associated with photosynthesis Compare Sun to Shade Leaves Anatomy of Sun leaves compared to Shade leaves -Cell Size, -Surface areas, -cuticle thickness, -thickness of palisade parenchyma (extra cell layer) -chloroplast per unit area Biochemistry of Sun leaves compared to Shade leaves -Chlorophyll per chloroplast -Nitrogen and Rubisco per unit area -Number of light harvesting complex per unit area -Chlorophyll per unit leaf area Gas Exchange of Sun leaves compared to Shade leaves -photosynthetic and respiratory capacity per unit area -photosynthetic capacity and respiration per unit dry mass -quantum yield WILLTHESE TRAITS INCREASE, DECREASE, OR REMAIN CONSTANT?

13. Cross-section of sun (L) and shade leaf (R) (C. album ) www.bio.sci.osaka-u.ac.jp/. ../high_reso.html Anatomy of Sun leaves compared to Shade leaves -smaller cells, -smaller surface and interveinal areas, -thicker cuticles, -thicker palisade parenchyma (extra cell layer) -More chloroplast per unit area Biochemistry of Sun leaves compared to Shade leaves -Chlorophyll per chloroplast is lower -Nitrogen and Rubisco per unit area is higher -Light harvesting complex per unit area is lower -Chlorophyll per unit leaf area is similar Gas Exchange of Sun leaves compared to Shade leaves -photosynthetic and respiratory capacity per unit area is higher -photosynthetic capacity and respiration per unit dry mass is similar -quantum yield is similar

14. Shade Mean Leaf Area cm2 Shade Sun leaves higher SLA (cm2 g-1) Sun Sun Elevation Elevation Mean leaf size of leaves of Northofagus. pumilio , collected at different altitudes at the volcano Lanin. Black points refer to shade leaves and yellow points to sun-exposed leaves. Specific leaf area (SLA) of leaves of Northofagus. pumilio , collected at different altitudes at the volcano Lanin. Black points refer to shade leaves and yellow points to sun-exposed leaves. www.uni-hohenheim.de/ ~franzari/UVB/haupt.htm

15. Sun vs. Shade leaves Why such changes! Sun Leaves (Maximize Carboxylation limitations) How? - Adding more cells and chloroplasts per leaf area! Thicker leaves - taller Palisade Cells and/or more layers Thicker cuticles to minimize water loss (sun is hot!) Shade Leaves (Minimize Light Limitations) More Spongy mesophyll - -air spaces increases the efficiency of light absorbance by influencing light scattering Invest more in light harvesting complex within chloroplast -to maximize what little light is available

16. (Light Reactions) Light Limiting Carboxylation Limited (Carbon reactions) What is changing in these plants in terms of allocation?

17. Influence of Temperature on Photosynthesis Thermal Acclimation and Adaptations

18. Temperature influences on Photosynthesis Open circles - Photosynthesis at 3kPa O2 Black circles - Photosynthesis at 18k Pa O2

19. Boltzmann Temperature response Kinetic processes= e-E/kT Enzymes denature Oxygenation reaction Biological Rate AOpt Carbon fixation reactions Temperature

20. Plants show ‘optimal’ temperature for photosynthesis -Optimal peak is close to normal growth temperature -Below optimum photosynthesis is limited by carbon fixation reactions -At high temperatures oxygenating reaction of Rubisco increases more than carboxylation photorespiration increasingly more important Why Photorespiration more important at high temps? - Solubility of CO2 decreases with increasing temperature More strongly than does O2 • temperature influences kinetic properties of Rubisco • (value of Km)

21. Shift in Amax with growing season temperature Evolutionary response In Amax within and between populations

22. ‘Plastic’ response of leaves grown in differing temperatures

23. Plants show an optimum temperature for Amax Adaptation to high temperatures • saturation of membrane lipids • (decreases membrane fluidity) At low temperatures (before freezing) chilling injury • Decrease in membrane fluidity • Change in the activity of membrane associated enzymes • And processes (electron transport slows down) -Loss of activity of cold-sensitive enzymes

24. Adaptations to cold temperatures -Increase concentrations of Rubisco -higher leaves of cytosolic Fru 1,6-bisphosphatase increase rates of Sucrose production -Rates of PSII activity can be altered (increased electron transport in colder environments)

25. Maximum rates of photosynthesis by arctic and alpine plants are similar to temperate and tropical species!

26. Mesic habitats Variation within and between species associated with variation in PSN capacity, leaf N content, leaf morphology/ontogeny Variation between species associated with adaptation to aridity (WUE ! ) Arid habitats Why Variability in Leaf Conductance and Photosynthetic Capacity? Range of leaf conductance Photosynthetic capacity Selection is acting to maximize dE/dA in differing environments

27. Problems with C3 photosynthesis Increase in photorespiration - in hot dry conditions Why? - Competition between O2 and CO2 for Rubisco binding site Photorespiration increases when [O2] / [CO2] inside the leaf increases

28. Photosynthetic Pathway Variation • Focus until now has been on C3 photosynthesis • Variation in biochemistry of photosynthesis exists and has ecological implications – CAM and C4 photosynthesis Biochemistry worked on by Hatch and Slack 1966 C4 and CAM are two evolutionary solutions to the problem of maintaining photosynthesis with stomata partially or completely closed on hot, dry days (Carbon Concentrating Adaptations)

29. Photosynthetic Pathway Variation • C3 – CO2 fixation by Rubisco; PGA (phosphoglycerate – a 3 carbon sugar) is the product of initial carboxylation • C4 – CO2 fixation by PEP carboxylase to produce OAA (oxaloacetate – a 4 carbon acid); C4 then transported within the leaf, decarboxylation and re-fixation by Rubisco. • CAM (crassulacean acid metabolism) – CO2 fixation by PEP carboxylase to OAA, but results in the production of malic acid in the vacuole during the day and de-carboxylation and fixation at night

30. C3, C4 and CAM • C4 photosynthesis results in CO2 concentrating at the site of carboxylation, by a spatial specialization of biochemistry – Kranz Anatomy (Bundle Sheath Design) • CAM photosynthesis results in CO2 concentration at the site of carboxylation by a temporal specialization of biochemistry

31. Central Steps in C4 photosynthesis Carboxylation of PEP (by PEP Carboxylase) produces C4 acids in the mesophyll cells (2) Organic acids are transported to the bundle sheath cells (3) Organic acids are decarboxylated in bundle sheath cells producing CO2 (4) CO2 is assimilated by Rubisco and PCR cycle (5) Compounds return to the mesophyll cells to regenerate more PEP

32. Anatomical differences between C3 and C4 plants www.plantphys.net/ article.php?ch=e&id=290 Comparison of leaf anatomy of C3 and C4 plants. Reproduced through the courtesy of Dr. Stephen Grace, University of Arkansas.

33. Anatomy of C4 plants Corn leaf cross-section www.unlv.edu/.../ Anatomy/Leaves/Leaves.html Kranz Anatomy (Bundle Sheath Design) Figure 2   Diagrams of Kranz anatomy in a C4 dicot and a C4 grass. (A) In the C4 dicot Atriplex rosea (NAD-ME), the bundle sheath cells form only a partial sheath around the vascular tissue. Only the radially arranged mesophyll cells that are in contact with the bundle sheath express PEPCase. (B) In the C4 grass Panicum capillare (NAD-ME), the large vascular bundles are surrounded by both a non-photosynthetic bundle sheath (mestome sheath) and the photosynthetic bundle sheath. www.plantphys.net/ article.php?ch=e&id=290

34. C4 plants have a mechanism to enhance the partial pressure of CO2 at the site of Rubisco - so that oxygenation reaction of Rubisco is virtually inhibited Mesophyll CO2 concentration 100 mmol mol-1 Bundle Sheath CO2 concentration 2000 mmol mol-1 C3 C3 Rubisco PCR (Calvin Cycle) PEP CO2 PEP Carboxylase CO2 CO2 C4 CHO C4

35. Three subtypes of C4 photosynthesis (!) Based on the enzyme involved in the decarboxylation of the C4 compounds transported to the vascular bundle sheath

36. The Compensation Point Compensation points for C3 and C4 differ Net Assimilation = gross photosynthesis - respiration http://www.steve.gb.com/science/photosynthesis_and_respiration.html

37. CAM Generally in Succulent Plants Cactaceae Bromeliaceae

38. The first recognition of the nocturnal acidification process(CAM) can be traced to the Romans, who noted that certain succulent plants taste more bitter in the morning than in the evening. (Rowley, 1978)

39. CAM photosynthesis results in CO2 concentration at the site of carboxylation by a temporal specialization of biochemistry

40. Comparing C3 and C4 photosynthesis CAM C4 The above diagram compares C4 and CAM C4 photosynthesis. Both adaptations are characterized by initial fixation of CO2 into an organic acid such as malate followed by transfer of the CO2 to the Calvin cycle. In C4 plants, such as sugarcane, these two steps are separated spatially; the two steps take place in two cell types. In CAM C4 plants, such as pineapple, the two steps are separated temporally (time); carbon fixation into malate occurs at night, and the Calvin cycle functions during the day. Both C4 and CAM C4 are two evolutionary solutions to the problem of maintaining photosynthesis with stomata partially or completely closed on hot, dry days. However, it should be noted, that in all plants, the Calvin cycle is used to make sugar from carbon dioxide.

41. CAM C4 PHOTOSYNTHESIS Dark CO2 concentration 150 mmol mol-1 Light CO2 concentration 4000 mmol mol-1 CHO CHO PEP PCR (Calvin Cycle) PEP Carboxylase CO2 CO2 C3 C4 (Malic Acid) Rubisco C4 CO2 Malic Acid Acidification of Vacuole

42. DARK Light CO2 Fixation = by BOTH PEP carboxylase and RUBISCO