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Plantenbiologie college 1 deel 2

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Plantenbiologie college 1 deel 2

  1. 2. Why is the rate of photosynthesis so much lower than expected ?
  2. 3. Waarom zoveel minder fotosynthese dan verwacht? <ul><li>Fotorespiratie </li></ul><ul><li>Inefficiëntie </li></ul><ul><li>Reflectie </li></ul><ul><li>Temperatuur </li></ul><ul><li>Limitatie resources </li></ul><ul><li>Verschil in chloroplasten (licht en donker) </li></ul><ul><li>Dikte cuticula </li></ul><ul><li>Licht valt langs bladeren </li></ul><ul><li>Overschaduwing / bladstand </li></ul><ul><li>Aantal huidmondjes </li></ul><ul><li>Slechte meting </li></ul>
  3. 4. 1. Dark respiration also happens during the day! Net photosynthesis = <ul><li>+ CO 2 -fixation </li></ul><ul><li>dark respiration </li></ul><ul><li>photorespiration </li></ul>
  4. 5. 2. The fate of light:
  5. 6. 2b. Absorptance of a chlorophyll solution: Abosorption chlorophyll at blue and red wavelengths
  6. 7. 2b. Absorptance of a chlorophyll solution: Abosorption chlorophyll at blue and red wavelengths
  7. 8. 2c. Absorptance of a leaf: 400 500 600 700 800 1.0 0.8 0.6 0.4 0.2 0.0 absorptance transmittance Fraction Wavelength (nm)  Wavelength dependency whole-leaf absorption less severe than chlorophyll solution
  8. 9. 400 500 600 700 800 1.0 0.8 0.6 0.4 0.2 0.0 Absorptance Wavelength (nm) 400 500 600 700 800 1.0 0.8 0.6 0.4 0.2 0.0 Transmittance Wavelength (nm) air oil oil air DeLucia et al, 1996 Air-filled intercellulair spaces allow for internal reflectance  more absorptance light
  9. 10. 3. Light limitation:
  10. 11. 3. Light limitation:
  11. 12. 4. CO 2 supply: = CO 2 compensatie punt
  12. 13. 4b. CO 2 extern > CO 2 intern CO 2 intern depends on stomatal opening and stomatal density
  13. 14. 4c. A-c i curve:
  14. 15. 5. Photorespiration: <ul><li>Carboxylation: </li></ul><ul><ul><li>RUBP + CO 2  2 C 3 </li></ul></ul>
  15. 16. 5. Photorespiration: <ul><li>Carboxylation: </li></ul><ul><ul><li>RUBP + CO 2  2 C 3 </li></ul></ul>Oxygenation: RUBP + O 2  1 C 3 + 1 C 2 2 C 2 + ATP  1 C 3 + CO 2
  16. 17. 5b. Photorespiration Phosphoglycolate + O 2 + ATP -> PGA + CO 2 + ADP + 2Pi G3P G3P G3P G3P G3P Chloroplast  peroxisome  mitochondria  peroxisome  chloroplast Fotorespiratie dus noodzakelijk om C 2 (PG) te regenereren
  17. 18. 6. Morpholoigcal & Physiological variation - Low- and high-light leaves: High light - thick leaf Many chloroplasts m -2  High [Rubisco] m -2 Low light - thin leaf Fewer chloroplasts m -2  Low [Rubisco] m -2
  18. 19. 6b. Photosynthetic machinery:
  19. 20. 6b. Photosynthetic machinery:
  20. 21. 6c. Light harvesting – low light vs. high light leaves Low light: Increase antennae for enhanced light harvesting
  21. 22. 6c. Light harvesting – low light vs. high light leaves Low light: Increase antennae for enhanced light harvesting
  22. 23. Why nett photosynthesis is constrained <ul><li>Not all wavelengths are equally well absorbed </li></ul><ul><li>Barrier for external CO 2 to reach chloroplasts </li></ul><ul><li>Light limitations and CO 2 limitations </li></ul><ul><li>Dark respiration respires photosynthates </li></ul><ul><li>Rubisco binds O 2  photorespiration needed, respiring photosynthates </li></ul><ul><li>Leaf anatomy & physiology can be suboptimal for max. photosynthesis </li></ul>
  23. 24. Conclusions Photosynthesis: <ul><li>Without photosynthesis there is no growth </li></ul><ul><ul><ul><li>(and no life either) </li></ul></ul></ul><ul><li>2. PS a may be modulated by external factors: light, CO 2 , temperature, water </li></ul><ul><li>3. Photorespiration can drastically reduce net photosynthesis </li></ul>
  24. 25. Simple experiment:
  25. 26. Simple experiment: <ul><li>Plants under a sealed cover: </li></ul><ul><ul><li>a. willow: † </li></ul></ul><ul><ul><li>b. maize: † </li></ul></ul><ul><ul><li>c. willow + maize: </li></ul></ul><ul><ul><li>willow † </li></ul></ul><ul><ul><li>maize </li></ul></ul>

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