1. Plant Stress
Next assignment for Friday, Feb 22: presenting an abiotic plant stressor, what is known about it, and how it might affect plants in an ~ 10 minute presentation.

2. / 18 Content / 2 Organization? / 1 Introduction?
/ 5 Quantity of material presented?
/ 5 Quality of material presented?
/ 2 Clarity?
/ 1 Understanding?
/ 2 use of images
  / 7 Mechanics
/ 1 Confidence
/1 Diction & volume
/ 1 Interaction with audience
/ 1 Pace
/ 1 poise, mannerisms
/ 1 Time?
/ 1 Quality of answers
Total: /25 = pts

3. We have chosen the following stresses:
Yelling
Shaking
Elevated CO2
Fungal stress
N and S deprivation
High Temp
Predation
Flooding
Each of you will make presentations and write a 5 page paper about something to do with the project.
Grading Proposal:  

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

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
only link: each provides
substrates for the other

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

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

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

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

10. 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

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

12. 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

13. 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

14. 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

15. 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

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

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

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

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

20. 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

21. 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

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

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

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

25. 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

26. 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

27. 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

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

29. 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

30. Z-scheme energetics

31. 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

32. 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+

33. 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

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

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

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

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

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

39. 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

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

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

42. 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

43. 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

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

45. 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)

46. 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

47. 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

48. 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

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

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

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

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

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

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

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

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

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

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

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

60. 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

61. Shown experimentally that need 4 flashes/O2

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

63. 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)

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

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

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

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

68. Electron transport from Ferredoxin to NADP+
2 Ferredoxin reduces
NADP reductase

69. Electron transport from Ferredoxin to NADP+
2 Ferredoxin reduces
NADP reductase
reduces NADP+

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

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

72. Chemiosmotic ATP synthesis
PMF mainly due to ∆pH
is used to make ATP

73. Chemiosmotic ATP synthesis
PMF mainly due to ∆pH
is used to make ATP
-> very little membrane
potential, due to transport
of other ions

74. 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

75. 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

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

77. 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

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

79. 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

80. 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!

81. 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

82. 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

83. 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

84. 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

85. 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

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

87. 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

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

89. 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

90. 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

91. 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

92. 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

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

94. 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

95. 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