1. Photoprotection in plants Plant Physiology Biology UNI PP11

2. Plant job description light H2OH2O CO 2 sugar O2O2 The good stuff?

3. Balanced photosynthesis PhotoSynthesis High energy compounds Harvests light energy Uses harvested energy Real time

4. Unbalanced photosynthesis Photo Synthesis High energy compounds bright light produces lots of energy low-capacity biochemical pathways use it slowly Real time Potential for destruction.

5. Photosynthetic electron flow ADP + Pi ATP H+H+ H+H+ H+H+ 3 H + NADPH PS IIPS I H 2 O split H2OH2O O2O2 Water splitting complex Cytochrome complex Thylakoid membrane Coupling factor e-e- e-e- e-e- e-e-

6. Too much energy in Biochemistry can’t use it Electrons pile up, high [O 2 ] Nasty compounds –O 2 -, 1 O 2 * (singlet oxygen) –H 2 O 2,. OH Oxidize chlorophyll (bleach) Oxidize lipids Can kill cells

7. Photoprotection Broadest sense Avoidance of excess energy into leaf –Plant & leaf angles –Reduce absorbtion Doing something harmless with the energy Unavoidable damage

8. Plant and leaf angles Most plants have characteristic angles Upright –Desert –High latitude trees –Crowded plants Prostrate –Cold –Icy winds

9. Leaves that move Adjust light interception (+/-)

10. Examples of avoidance

11. Light meets leaf Reflected Absorbed Transmitted All of the light is reflected, absorbed or transmitted.

12. Increasing reflection White top surface –Hair –Wax –Air layers White bottom surface –Reflect externally –Reflect internally

13. Increase transmittance Move and turn chloroplasts

14. Photosystem geometry Light harvesting complex Reaction center

15. Shade and sun plants Sun plant Shade plant Genetic control (capacity) and developmental control. May not be able to adjust later.

16. Where the energy can go Phytochemistry (synthesis half) Dissipated –Fluorescence of chlorophyll (red) –Transferred to carotenoids or xanthophylls Yellow pigments –Most carotenoids (constituitive) –Xanthophylls (“cycle” or seasonal) Can go on to make harmful O 2 species

17. Chlorophyll fluorescence

18. Carotenoids Grab excitation energy from chlorophyll Turns down the “volume” on chl excitation Beta-carotene –Always found with chlorophyll –Split in half to make Vitamin A Lutein –Retinal protection Xanthophylls

19. 3 kinds –Violaxanthin (nonprotective) –Antheroxanthin (protective) –Zeaxanthin (protective) Interconvert –Photoprotective forms in high light –Violaxanthin in low light –Proportional, constantly adjusted –Cycles (shuttles) back & forth

20. Out in nature Conifers in winter –High light, low chemistry –High levels of photoprotective forms Sun plants –Shuttle back and forth, day to night Shade plants –May make & keep for day after sunfleck Pool sizes vary

21. Visualizing xanthophyll action Light curve High light plant Photo-limited part Synthesis-limited part Saturation Reduction at high light Time scale: minutes Xanthophylls or damage?

22. Failure to protect PS II rxn center vulnerable O 2 generated No other protection D1 protein degraded in light –Part of light harvesting complex (LHC) –Disassemble (LHC), trade proteins, reassemble –Always happening in light –More light, more degradation Can’t keep up? Capacity for photosynthesis drops

23. Problem solving at every level Plant orientation Leaf orientation Leaf spectral characteristics Protective pigments –Constituitive –Induced Repair Sometimes it still fails

24. Too much of a good thing light H2OH2O CO 2 sugar O2O2