1. Plant defense responses Hypersensitive response
Prepare a 10’ talk for Friday March 3 on plant defense responses or describe interactions between plants& pathogens, pests or symbionts
Plant defense responses
Hypersensitive response
Systemic acquired resistance
Innate immunity
Phytoalexin synthesis
Defensins and other proteins
Oxidative burst
Some possible pests
Nematodes
Rootworms
Aphids
Thrips
Gypsy moths
hemlock woolly adelgid
Some possible pathogens
Agrobacterium tumefaciens
Agrobacterium rhizogenes
Pseudomonas syringeae
Pseudomonas aeruginosa
Viroids
DNA viruses
RNA viruses
Fungi
Oomycetes
Some possible symbionts
N-fixing bacteria
N-fixing cyanobacteria
Endomycorrhizae
Ectomycorrhizae

2. Converts light to chemical energy
Photosynthesis
Converts light to chemical energy
6 CO2 + 6 H2O + light energy <=> C6H12O6 + 6 O2

3. Photosynthesis
2 sets of rxns in separate
parts of chloroplast

4. PSI works by itself in cyclic photophosphorylation
PSI gives excited e- to Fd
Fd returns e- to P700+ via PQ, cyt b6/f & PC
Each e- pumps H+ at cyt b6/f
Use PMF to make ATP

5. PSI and PSII work together in the “Z-scheme”
PSII gives excited e- to ETS ending at NADPH
Each e- drives cyt b6/f
Use PMF to make ATP
PSII replaces e- from H2O forming O2

6. Physical organization of Z-scheme
2 mobile carriers
1) plastoquinone
2) plastocyanin (PC)
3 protein complexes
1) PSI
2) PSII
3) cytochrome b6/f
ATP synthase (CF0-CF1
ATPase) is also visible
in E/M

7. Physical organization of Z-scheme
Complexes are arranged asymmetrically!
PSII is in appressed regions of grana
PSI and ATP synthase in exposed regions
cytochrome b6/f, PC and PQ are evenly dispersed
why PC and PQ must be mobile
why membrane must be very fluid

8. Chemiosmotic ATP synthesis
PMF mainly due to ∆pH
is used to make ATP
-> very little membrane
potential, due to transport
of other ions
thylakoid lumen pH is < 5
cf stroma pH is 8
pH is made by ETS, cyclic
photophosphorylation,water
splitting & NADPH synth

9. Chemiosmotic ATP synthesis
Structure of ATP synthase
CF1 head: exposed to
stroma
CF0 base: Integral
membrane protein

10. a & b2 subunits form stator that immobilizes a & b F1 subunits
a is also an H+ channel
c subunits rotate as H+
pass through
g & e also rotate
c, g & e form a rotor

11. Binding Change mechanism of ATP synthesis
H+ translocation through ATP synthase alters affinity of active site for ATP

12. Binding Change mechanism of ATP synthesis
H+ translocation through ATP synthase alters affinity of active site for ATP
ADP + Pi bind to  subunit
then spontaneously form ATP

13. Binding Change mechanism of ATP synthesis
H+ translocation through ATP synthase alters affinity of active site for ATP
ADP + Pi bind to  subunit
then spontaneously form ATP
∆G for ADP + Pi = ATP is ~0
role of H+ translocation is to
force enzyme to release ATP!

14. Binding Change mechanism of ATP synthesis
1) H+ translocation alters affinity of active site for ATP
2) Each active site ratchets through 3 conformations that have different affinities for ATP, ADP & Pi
due to interaction with the subunit

15. Binding Change mechanism of ATP synthesis
1) H+ translocation alters affinity of active site for ATP
2) Each active site ratchets through 3 conformations that have different affinities for ATP, ADP & Pi
3) ATP is synthesized by rotational catalysis
g subunit rotates as H+ pass through Fo, forces each active site to sequentially adopt the 3 conformations

16. Evidence supporting chemiosmosis
1) ionophores (uncouplers)
2) can synthesize ATP if create ∆pH
a) Jagendorf expt: soak cp in pH 4 in dark, make ATP when transfer to pH 8

17. Evidence supporting chemiosmosis
Racker & Stoeckenius (1974) reconstituted bacteriorhodopsin and ATP synthase in liposomes
Bacteriorhodopsin uses light to pump H+
make ATP only
in the light

18. Evidence supporting “rotational catalysis”
Sambongi et al experiment
a) reconstituted ATPase & attached a subunits to a slide
b) attached actin filament to c subunit & watched it spin

19. Regulating Light reactions
Regulate partitioning of light energy between PSI and PSII by phosphorylating LHCII complex
ordinarily is associated with PSII.

20. Regulating Light reactions
Regulate partitioning of light energy between PSI and PSII by phosphorylating LHCII complex
ordinarily is associated with PSII.
if PSI falls behind PSII LHCII is kinased

21. Regulating Light reactions
if PSI falls behind PSII LHCII is phosphorylated
increased negative charge forces it out of appressed stacks

22. Regulating Light reactions
if PSI falls behind PSII LHCII is phosphorylated
increased negative charge forces it out of appressed stacks
it then associates with PSI & boosts PSI cyclic activity

23. Regulating Light reactions
if PSI falls behind PSII LHCII is phosphorylated
increased negative charge forces it out of appressed stacks
it then associates with PSI & boosts PSI cyclic activity sensor is PQ: when highly reduced it indirectly activates a protein kinase that kinases LHCII

24. Regulating Light reactions
sensor is PQ: when highly reduced it indirectly activates a protein kinase that kinases LHCII
elevated PQH2 means PSI is falling behind

25. Regulating Light reactions
sensor is PQ: when highly reduced it indirectly activates a protein kinase that kinases LHCII
elevated PQH2 means PSI is falling behind
Allows plants to adjust relative ATP & NADPH syn

26. Regulating ATP synthase
in dark, ATP synthase could
run backwards and consume
ATP to make a PMF

27. Regulating ATP synthase
in dark, ATP synthase could
run backwards and consume
ATP to make a PMF
2 mechanisms prevent this
1) ATP synthase needs a
pH gradient to be active

28. Regulating ATP synthase
in dark, ATP synthase could
run backwards and consume
ATP to make a PMF
2 mechanisms prevent this
1) ATP synthase needs a
pH gradient to be active
2) ATP synthase must be
reduced by ferredoxin
(via thioredoxin) to be active
becomes oxidized (therefore
inactive) in the dark

29. Photoinhibition
Most plants are saturated at 1/4 full sunlight

30. Photoinhibition
Most plants are saturated at 1/4 full sunlight
Excess will damage
photosystems

31. Photoinhibition
Most plants are saturated at 1/4 full sunlight
Excess will damage
photosystems
D1 of PSII is fuse: first item to break in high light

32. Photoinhibition
Most plants are saturated at 1/4 full sunlight
Excess will damage
photosystems
D1 of PSII is fuse: first item to break in high light= photoinhibition

33. Photoinhibition
D1 of PSII is fuse: first item to break in high light= photoinhibition
Avoidance?

34. photoinhibition
Avoidance?
Carotenoids"quench" excited electrons

35. photoinhibition
Avoidance?
Carotenoids"quench" excited electrons
Dissipate excess energy as heat

36. photoinhibition
Avoidance?
Carotenoids"quench" excited electrons
Dissipate excess energy as heat
Violaxanthin sends exciton to PS

37. photoinhibition
Avoidance?
Carotenoids"quench" excited electrons
Dissipate excess energy as heat
Violaxanthin sends exciton to PS
Zeaxanthin dumps energy as heat

38. photoinhibition
Violaxanthin sends exciton to PS
Zeaxanthin dumps energy as heat
Convert Violaxanthin to Zeaxantin under high light

39. photoinhibition
Violaxanthin sends exciton to PS
Zeaxanthin dumps energy as heat
Convert Violaxanthin to Zeaxantin under high light
Use NADPH to revert Zeaxanthin to Violanthin in low light

40. photoinhibition
Violaxanthin sends exciton to PS
Zeaxanthin dumps energy as heat
Convert Violaxanthin to Zeaxantin under high light
Revert Zeaxanthin to Violanthin in low light
Other mechs : paraheliotropism, anthocyanins

41. Light-independent (dark) reactions
The Calvin cycle

42. Light-independent (dark) reactions
occur in the stroma of the chloroplast (pH 8)
Consumes ATP & NADPH from light reactions
regenerates ADP, Pi and NADP+

43. Light-independent (dark) reactions
Overall Reaction:
3 CO2 + 3 RuBP + 9 ATP + 6 NADPH =
3 RuBP + 9 ADP + 9 Pi + 6 NADP+ + 1 Glyceraldehyde 3-P

44. Light-independent (dark) reactions
1) fixing CO2
2) reversing glycolysis
3) regenerating RuBP

45. fixing CO2
1) RuBP binds CO2

46. fixing CO2
RuBP binds CO2
2) rapidly splits into two 3-Phosphoglycerate
therefore called C3 photosynthesis

47. fixing CO2
1) CO2 is bound to RuBP
2) rapidly splits into two 3-Phosphoglycerate
therefore called C3 photosynthesis
detected by immediately killing cells fed 14CO2

48. fixing CO2
1) CO2 is bound to RuBP
2) rapidly splits into two 3-Phosphoglycerate
3) catalyzed by Rubisco (ribulose 1,5 bisphosphate carboxylase/oxygenase)
the most important & abundant protein on earth

49. fixing CO2
1) CO2 is bound to RuBP
2) rapidly splits into two 3-Phosphoglycerate
3) catalyzed by Rubisco (ribulose 1,5 bisphosphate carboxylase/oxygenase)
the most important & abundant protein on earth
Lousy Km

50. fixing CO2
1) CO2 is bound to RuBP
2) rapidly splits into two 3-Phosphoglycerate
3) catalyzed by Rubisco (ribulose 1,5 bisphosphate carboxylase/oxygenase)
the most important & abundant protein on earth
Lousy Km
Rotten Vmax!

51. Reversing glycolysis
converts 3-Phosphoglycerate to G3P
consumes 1 ATP & 1 NADPH

52. Reversing glycolysis
G3P has 2 possible fates
1) 1 in 6 becomes (CH2O)n

53. Reversing glycolysis
G3P has 2 possible fates
1) 1 in 6 becomes (CH2O)n
2) 5 in 6 regenerate RuBP