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. Photosynthesis
1) Light rxns
use light to pump H+
use ∆ pH to make ATP by chemiosmosis

5. Photosynthesis
1) Light rxns
use light to pump H+
use ∆ pH to make ATP by chemiosmosis
2) Light-independent
(dark) rxns use ATP &
NADPH from light rxns
to make organics

6. Photosynthesis
1) Light rxns
use light to pump H+
use ∆ pH to make ATP by chemiosmosis
2) Light-independent
(dark) rxns use ATP &
NADPH from light rxns
to make organics
only link: each provides
substrates needed by the
other

7. Light Rxns
3 stages
1) Catching a photon (primary photoevent)

8. Light Rxns
3 stages
1) Catching a photon (primary photoevent)
2) ETS

9. Light Rxns
3 stages
1) Catching a photon (primary photoevent)
2) ETS
3) ATP synthesis by chemiosmosis

10. Catching photons
photons: particles of energy that travel as waves
Energy inversely proportional to wavelength ()
visible light ranges from nm

11. Catching photons
Photons: particles of energy that travel as waves
caught by pigments: molecules that absorb light

12. Pigments
Can only absorb certain photons

13. Pigments
Can only absorb certain photons
Photon has exact energy to push an e- to an outer orbital

14. Pigments
Can only absorb certain photons
Photon has exact energy to push an e- to an outer orbital
from ground to excited state

15. Pigments
Photon has exact energy to push an e- to an outer orbital
from ground to excited state
each pigment has an absorption spectrum: l it can absorb

16. Pigments
Chlorophyll a is most abundant pigment
chlorophyll a looks green
-> absorbs all l but green
Reflects green

17. Accessory Pigments
absorb l which chlorophyll a misses
chlorophyll b is an important
accessory pigment

18. Accessory Pigments
absorb l which chlorophyll a misses
chlorophyll b is an important accessory pigment
others include xanthophylls & carotenoids

19. Accessory Pigments
action spectrum shows use of accessory pigments
l used for photosynthesis

20. Accessory Pigments
action spectrum shows use of accessory pigments
l used for photosynthesis
plants use entire visible spectrum
l absorbed by chlorophyll work best

21. Light Reactions
1) Primary photoevent: pigment absorbs a photon

22. Light Reactions
1) Primary photoevent: pigment absorbs a photon
e- is excited -> moves to outer orbital

23. Light Reactions
4 fates for excited e-:
1) returns to ground state emitting heat & longer  light = fluorescence

24. Light Reactions
4 fates for excited e-:
1) fluorescence
2) transfer to another molecule

25. Light Reactions
4 fates for excited e-:
1) fluorescence
2) transfer to another molecule
3) Returns to ground state dumping energy as heat

26. 4 fates for excited e-:
1) fluorescence
2) transfer to another molecule
3) Returns to ground state dumping energy as heat
4) energy is transferred by inductive resonance
excited e- vibrates and induces adjacent e- to vibrate at same frequency

27. 4 fates for excited e-:
4) energy is transferred by inductive resonance
excited e- vibrates and induces adjacent e- to vibrate at same frequency
Only energy is transferred

28. 4 fates for excited e-:
4) energy is transferred by inductive resonance
excited e- vibrates and induces adjacent e- to vibrate at same frequency
Only energy is transferred
e- returns to ground state

29. Photosystems
Pigments are bound to proteins arranged in thylakoids in photosystems
arrays that channel energy absorbed by any pigment to rxn center chlorophylls

30. Photosystems
Pigments are bound to proteins arranged in thylakoids in photosystems
arrays that channel energy absorbed by any pigment to rxn center chls
Need 2500 chlorophyll to make 1 O2

31. Photosystems
Arrays that channel energy absorbed by any pigment to rxn center chls
2 photosystems : PSI & PSII
PSI rxn center chl a dimer absorbs 700 nm = P700

32. Photosystems
Arrays that channel energy absorbed by any pigment to rxn center chls
2 photosystems : PSI & PSII
PSI rxn center chl a dimer absorbs 700 nm = P700
PSII rxn center chl a dimer
absorbs 680 nm = P680

33. Photosystems
Each may have associated LHC (light harvesting complex) (LHC can diffuse within membrane)
PSI has LHCI: ~100 chl a, a few chl b & carotenoids

34. Photosystems
Each may have associated LHC (light harvesting complex) (LHC can diffuse within membrane)
PSI has LHCI: ~100 chl a, a few chl b & carotenoids
PSII has LHCII: ~250 chl a, many chl b & carotenoids
Proteins of LHCI & LHCII also differ

35. Photosystems
PSI performs cyclic photophosphorylation
Absorbs photon & transfers energy to P700

36. cyclic photophosphorylation
Absorbs photon & transfers energy to P700
transfers excited e- from P700 to fd

37. cyclic photophosphorylation
Absorbs photon & transfers energy to P700
transfers excited e- from P700 to fd
fd returns e- to
P700 via PQ,
cyt b6/f & PC

38. cyclic photophosphorylation
Absorbs photon & transfers energy to P700
transfers excited e- from P700 to fd
fd returns e- to P700 via PQ, cyt b6/f & PC
Cyt b6/f pumps H+

39. Cyclic Photophosphorylation
Transfers excited e- from P700 to fd
Fd returns e- to P700 via cyt b6-f & PC
Cyt b6-f pumps H+
Use PMF to make
ATP

40. Cyclic photophosphorylation
first step is from P700 to A0 (another chlorophyll a)
charge separation prevents e- from returning to ground state = true photoreaction

41. Cyclic photophosphorylation
first step is from P700 to A0 (another chlorophyll a)
next transfer e- to A1 (a phylloquinone)
next = 3 Fe/S proteins

42. Cyclic photophosphorylation
first step is from P700 to A0 (another chlorophyll a)
next transfer e- to A1 (a phylloquinone)
next = 3 Fe/S proteins
finally ferredoxin

43. Cyclic photophosphorylation
Ferredoxin = branchpoint: in cyclic PS FD reduces PQ

44. Cyclic photophosphorylation
Ferredoxin reduces PQ
PQH2 diffuses to cyt b6/f
2) PQH2 reduces cyt b6 and Fe/S, releases H+ in lumen
since H+ came from stroma, transports 2 H+ across membrane (Q cycle)

45. Cyclic photophosphorylation
3) Fe/S reduces plastocyanin via cyt f
cyt b6 reduces PQ to form PQ-

46. Cyclic photophosphorylation
4) repeat process, Fe/S reduces plastocyanin via cyt f
cyt b6 reduces PQ- to form PQH2

47. Cyclic photophosphorylation
4) repeat process, Fe/S reduces plastocyanin via cyt f
cyt b6 reduces PQ- to form PQH2
Pump 4H+ from stroma to lumen at each cycle (per net PQH2)

48. Cyclic photophosphorylation
5) PC (Cu+) diffuses to PSI,
where it reduces an oxidized P700

49. Cyclic photophosphorylation
energetics:
light adds its energy to e-
-> excited state
Eo' P700 = V
Eo' P700* = -1.3 V

50. Cyclic photophosphorylation
energetics:
light adds its energy to e-
-> excited state
Eo' P700 = V
Eo' P700* = -1.3 V
Eo' fd = V

51. Cyclic photophosphorylation
energetics:
light adds its energy to e-
-> excited state
Eo' P700 = V
Eo' P700* = -1.3 V
Eo' fd = V
Eo' cyt b6/f = +0.3V

52. Cyclic photophosphorylation
energetics:
light adds its energy to e-
-> excited state
Eo' P700 = V
Eo' P700* = -1.3 V
Eo' fd = V
Eo' cyt b6/f = +0.3V
Eo' PC = +0.36V

53. Cyclic photophosphorylation
energetics:
light adds its energy to e-
-> excited state
Eo' P700 = V
Eo' P700* = -1.3 V
Eo' fd = V
Eo' cyt b6/f = +0.3V
Eo' PC = +0.36V
e- left in excited state
returns in ground state

54. Cyclic photophosphorylation
e- left in excited state
returns in ground state
Energy pumped H+

55. Cyclic photophosphorylation
Limitations
Only makes ATP

56. Cyclic photophosphorylation
Limitations
Only makes ATP
Does not supply electrons for biosynthesis = no reducing power

57. Photosystems
PSI performs cyclic photophosphorylation
Makes ATP but not NADPH: exact mech for PQ reduction unclear,
but PQ pumps H+

58. Photosystem II
Evolved to provide reducing power
-> added to PSI

59. Photosystem II
Evolved to provide reducing power
Added to PSI
rxn center absorbs 680 nm (cf 700 nm)

60. Photosystem II
rxn center absorbs 680 nm (cf 700 nm)
can oxidize H2O
redox potential of P680+ is
+ 1.1 V (cf V for H2O)

61. Photosystem II
rxn center absorbs 680 nm (cf 700 nm)
can oxidize H2O
redox potential of P680+ is V (cf V for H2O)
Use e- from H2O to reduce
NADP+ (the e- carrier used
for catabolic reactions)

62. Photosystem II
rxn center absorbs 680 nm (cf 700 nm)
can oxidize H2O
redox potential of P680+ is V (cf V for H2O)
Use e- from H2O to reduce
NADP+ (the e- carrier used
for catabolic reactions)
use NADPH c.f. NADH
to prevent cross-
contaminating catabolic
& anabolic pathways

63. PSI and PSII work together in the “Z-scheme”
- a.k.a. “non-cyclic photophosphorylation”
General idea: ∆ redox potential from H2O to NADP+ is so great that must boost energy of H2O e- in 2 steps

64. PSI and PSII work together in the “Z-scheme”
General idea: ∆ redox potential from H2O to NADP+ is so great that must boost energy of H2O e- in 2 steps
each step uses a photon

65. PSI and PSII work together in the “Z-scheme”
General idea: ∆ redox potential from H2O to NADP+ is so great that must boost energy of H2O e- in 2 steps
each step uses a photon
2 steps = 2 photosystems

66. PSI and PSII work together in the “Z-scheme”
1) PSI reduces NADP+

67. PSI and PSII work together in the “Z-scheme”
1) PSI reduces NADP+
e- are replaced by PSII

68. PSI and PSII work together in the “Z-scheme”
2) PSII gives excited e- to ETS ending at PSI

69. PSI and PSII work together in the “Z-scheme”
2) PSII gives excited e- to ETS ending at PSI
Each e- drives cyt b6/f

70. PSI and PSII work together in the “Z-scheme”
2) PSII gives excited e- to ETS ending at PSI
Each e- drives cyt b6/f
Use PMF to make ATP

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

72. PSI and PSII work together in the “Z-scheme”
Light absorbed by PS II makes ATP
Light absorbed by PS I makes reducing power

73. Ultimate e- source None water O2 released? No yes
cyclic non-cyclic
Ultimate e- source None water
O2 released? No yes
Terminal e- acceptor None NADP+
Form in which energy is ATP ATP &
temporarily captured NADPH
Photosystems required PSI PSI & PSII

74. Z-scheme energetics

75. Physical organization of Z-scheme
PS II consists of: P680 (a dimer of chl a)
~ 30 other chl a & a few carotenoids
> 20 proteins
D1 & D2 bind P680 & all e- carriers

76. Physical organization of Z-scheme
PSII has 2 groups of closely associated proteins
1) OEC (oxygen evolving complex)
on lumen side, near rxn center
Ca2+, Cl- & 4 Mn2+

77. Physical organization of Z-scheme
PSII also has two groups of closely associated proteins
1) OEC (oxygen evolving complex)
on lumen side, near rxn center
Ca2+, Cl- & 4 Mn2+
2) variable numbers of LHCII complexes

78. Physical organization of Z-scheme
D1 & D2 bind P680 & all e- carriers
Synechoccous elongatus associates phycobilisomes cf LHCII with PSII

79. Physical organization of Z-scheme
D1 & D2 bind P680 & all e- carriers
Synechoccous elongatus associates phycobilisomes cf LHCII with PSII

80. Physical organization of Z-scheme
2 mobile carriers
plastoquinone : lipid similar
to ubiquinone

81. Physical organization of Z-scheme
2 mobile carriers
1) plastoquinone : lipid
similar to ubiquinone
“headgroup” alternates
between quinone & quinol

82. Physical organization of Z-scheme
2 mobile carriers
1) plastoquinone : lipid
similar to ubiquinone
“headgroup” alternates
between quinone & quinol
Carries 2 e- & 2 H+

83. Physical organization of Z-scheme
2 mobile carriers
1) plastoquinone : hydrophobic molecule like ubiquinone
“headgroup” alternates between quinone and quinol
Carries 2 e- & 2 H+
diffuses within bilayer

84. Physical organization of Z-scheme
2 mobile carriers
1) plastoquinone
2) plastocyanin (PC) : peripheral membrane protein of thylakoid lumen

85. Physical organization of Z-scheme
2) plastocyanin (PC) : peripheral membrane protein of thylakoid lumen
Cu is alternately oxidized & reduced
carries 1 e- & 1 H+

86. Physical organization of Z-scheme
3 protein complexes (visible in EM of thylakoid)
1) PSI
2) PSII
3) cytochrome b6/f
2 cytochromes & an Fe/S protein

87. 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

88. Physical organization of Z-scheme
3 protein complexes (visible in EM of thylakoid)
1) PSI
2) PSII
3) cytochrome b6/f
2 cytochromes & an Fe/S protein

89. 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

90. Physical organization of Z-scheme
Complexes are arranged asymmetrically!
PSII is in appressed regions of grana

91. Physical organization of Z-scheme
Complexes are arranged asymmetrically!
PSII is in appressed regions of grana
PSI and ATP synthase are found in exposed regions (ends & margins of grana, and stromal lamellae)

92. Physical organization of Z-scheme
Complexes are arranged asymmetrically!
PSII is in appressed regions of grana
PSI and ATP synthase are in exposed regions
cytochrome b6/f, PC and PQ are evenly dispersed

93. 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

94. 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

95. PSII Photochemistry
1) LHCII absorbs a photon
2) energy is transferred to P680

96. PSII Photochemistry
3) P680* reduces pheophytin ( chl a with 2 H+ instead of Mg2+) = primary electron acceptor

97. PSII Photochemistry
3) P680* reduces pheophytin ( chl a with 2 H+ instead of Mg2+) = primary electron acceptor
charge separation traps the electron

98. PSII Photochemistry
4) pheophytin reduces PQA (plastoquinone bound to D2)
moves electron away from
P680+ & closer to stroma

99. PSII Photochemistry
5) PQA reduces PQB (forms PQB- )

100. PSII Photochemistry
6) P680+ acquires another electron ,
and steps 1-4 are repeated

101. PSII Photochemistry
7) PQA reduces PQB - -> forms PQB2-

102. PSII Photochemistry
8) PQB2- acquires 2 H+ from stroma
forms PQH2 (and adds to ∆pH)

103. PSII Photochemistry
9) PQH2 diffuses within bilayer to cyt b6/f
- is replaced within D1 by an oxidized PQ

104. Photolysis: Making Oxygen
1) P680+ oxidizes tyrZ ( an amino acid of protein D1)

105. Photolysis: Making Oxygen
2) tyrZ + oxidizes one of the Mn atoms in the OEC
Mn cluster is an e- reservoir

106. Photolysis: Making Oxygen
2) tyrZ + oxidizes one of the Mn atoms in the OEC
Mn cluster is an e- reservoir
Once 4 Mn are oxidized replace e- by
stealing them from 2 H2O

107. Shown experimentally that need 4 flashes/O2

108. Shown experimentally that need 4 flashes/O2
Mn cluster cycles S0 -> S4
Reset to S0 by taking 4 e-
from 2 H2O

109. Electron transport from PSII to PSI
1) PQH2 diffuses to cyt b6/f
2) PQH2 reduces cyt b6 and Fe/S, releases H+ in lumen
since H+ came from stroma, transports 2 H+ across membrane (Q cycle)

110. Electron transport from PSII to PSI
3) Fe/S reduces plastocyanin via cyt f
cyt b6 reduces PQ to form PQ-

111. Electron transport from PSII to PSI
4) repeat process, Fe/S reduces plastocyanin via cyt f
cyt b6 reduces PQ- to form PQH2

112. Electron transport from PSII to PSI
4) PC (Cu+) diffuses to PSI,
where it reduces an oxidized P700

113. Electron transport from PSI to Ferredoxin
1) LHCI absorbs a photon
2) P700* reduces A0
3) e- transport to ferredoxin via
A1 & 3 Fe/S proteins

114. Electron transport from Ferredoxin to NADP+
2 Ferredoxin reduce
NADP reductase

115. Electron transport from Ferredoxin to NADP+
2 Ferredoxin reduce
NADP reductase
reduces NADP+

116. Electron transport from Ferredoxin to NADP+
2 Ferredoxin reduce
NADP reductase
reduces NADP+
this also contributes
to ∆pH

117. Overall reaction for the Z-scheme
8 photons + 2 H2O
+ 10 H+stroma + 2 NADP+
= 12 H+lumen + 2 NADPH
+ O2