# Presentation: 469194

## The Architecture Of Photosynthesis

**is Optimized to:**

**Cover the solar spectrum**
**Protect against photochemical damage**

**Separate energy and electron **
**transfer**

**Regulate the efficiency of light**
**harvesting and repair**
** ****damage (PSII)**

**Transmit excitation to the**
**reaction center with near **
**efficiency**

## A Pragmatic Answer:

**An Abstract Question: **
**How much Chl is in Picasso’s tree ?**

**A Collection of Facts**

- Pablo Picasso – House and Trees
-          Paris, Winter 1908

-        A “medium” size tree has
-             ~ 100,000 leaves
-    An “average” leaf has a surface
-                     area of
-               ~ 2.8 x 10-3  m2
-    The “average” Chl content of a C3
-                      leaf is
-            ~ 5.6 x 10-4 mol m-2
-       The molecular weight of Chl *a* is
-                    894 g/ mol

**A Pragmatic Answer:**
**    **
**    ****140 g Chl / tree**

- http://www.hipernet.ufsc.br/wm/paint/auth/picasso/landscapes/picasso.house-garden.jpg

##   How many special pair Chls are in Picasso’s tree?

**  ****How many special pair Chls are in Picasso’s tree?**

**140 g Chl / tree**
**2 “special pair” Chls          **
**      ****initiate primary    **
**      ****photochemistry**
**~ 0.5 g Chl special Chls /**
**	****	****tree**
**How can this be explained ?**

- Photosynthetic
- Reaction Center
- (RC)

## Light Harvesting Timescales

**Light Harvesting Timescales**

## Current Model of the PSU 

**Current Model of the PSU**

_**Net Reaction of PSI and PSII:**_
_**ATP synthase**_**: Uses electrochemical potential to synthesize ATP from ADP**

_**Net Reaction of the **_
_**Calvin Cycle: **_

## Photosynthetic organisms experience

**excessive light on a daily basis**

**excess light**

**rate of light absorption**

**rate of photosynthesis**

**incident light intensity**

## Pigments From a Portion of the LH2 Ring

**RG1****A**

**RG1****B**

**B800****B**

**B800****A**

******B850****B**

******B850****A**

**RG2****B**

**RG2****A**

## Photosynthetic organisms experience frequent short-term fluctuations in light intensity.

- Külheim et al. (2002) Science _297_: 91-93

## Photosystem II—3.5 Å

**Photosystem II—3.5 ****Å**

- K. N. Ferreira, T. M. Iverson,
- K. Maghlaoui, J. Barber and
- S. Iwata. Science. In Press.
- (2004)

- D1 = yellow
- D2 = orange

## Models for Repair of PSII—D1 Protein

**Models for Repair of PSII—D1 Protein**

- E. Baena-Gonzalez and E.-M. Aro.
*Phil . Trans. R. Soc. Lond. B*, **357**,
- 1451-1460 (2002).

- P. Silva et. al. *Phil . Trans. R. Soc. *
*Lond. B*, **357**, 1461-1468 (2002).

## Photoprotection involves regulation

**PS II**

**thylakoid membrane**

**lumen**

**stroma**

**light**

**heat ****(nonphotochemical quenching)**

**photochemistry**

**peripheral**
**LHC**

**inner**
**LHC**

**COO****-**

**COO****-**

**H****+**

**PS II**

**inner**
**LHC**

**short term**
**regulation**

**long term**
**regulation**

**Photoprotection involves regulation**
** ****of light harvesting  **

**LHC**
**protonation**

**zeaxanthin**
**synthesis**

**and**

**PQH****2**

**regulation of nuclear**
**LHC gene expression**

## Photosystem II Supercomplex

## What is NPQ?

-     Nonradiative energy dissipation in PSII
-              _Purpose_: protects PSII from photochemical damage
-              _Main Component_:  **q****e** - “high energy state quenching”

- High Light (10-20 min.) = Decrease in F  (~50%)

## Necessary components for qE

- a.

- b.

**Necessary components for q****E**
-      a. ∆pH
-       b. Zeaxanthin
-       c. PsbS

## Molecular genetic analysis of npq4-1

**Molecular genetic analysis of *****npq4-1***
**showed that PsbS is necessary for qE.**

**4.4 kb**

**genomic DNA**
**hybridization with *****psbS***

**wild type**

***npq4-1***

## qE is more than two times greater

**in the transgenic plants**

**wild type (2 copies of *****psbS******)***

***npq4-1***** (no *****psbS)***

**wt+one *****psbS***** gene #17 (4 copies of *****psbS)***

**wt+one *****psbS***** gene #5 (4 copies of *****psbS)***

**wild type**
**qE =1.3**

**transgenic**
**plants**
**qE =2.9**** **

## 	     Transient Absorption Experiment

- Chl *a*

**Energy (cm****-1****)**

**Car **

**Car **

**NPQ**

**No NPQ**

- Qy

-    Qx

**Absorption**

-  **S****o ****(****1****A****g****)**

**S****2 ****(**** ****1****B****u****)**

- So

-  **S****n**

- Soret

- Pump

- Probe

- kET

**S****1 ****(****1****A****g****)**

-  **(****1****A****g****)**** S****o**

-  **(****1****A****g****)**** S****1**

** ****(**** ****1****B****u****)**** S****2**

- 	     **Transient Absorption Experiment**

##             Transient Absorption Measurements             on Arabidopsis Mutants

**Light ON**

**Light OFF**

- 0

- 10

- 20

- 30

- 40

- 50

- 0

- 1

- 2

- 3

**   *****wild type***

- regular qE

- Time (ps)

- 0

- 10

- 20

- 30

- 40

- 50

- 0

- 1

- 2

- 3

**     *****npq4- E122Q E226Q***

** **

- more PsbS

*, *

- but a

*                           *nonfunctional

*                         *

- version no qE

- Time (ps)

- 0

- 10

- 20

- 30

- 40

- 50

- Amplitude (a.u.)

- 0

- 1

- 2

- 3

- 0

- 10

- 20

- 30

- 40

- 50

- Amplitude (a.u.)

- 0

- 1

- 2

- 3

**          *****wild type + PsbS***

- more PsbS and

*                        *more qE than wt

**        *****npq4-1***

- no PsbS

*            *no qE

- Quenched * 1.9

- Quenched * 1.3

******pump ****= 664 nm**
******probe ****= 540 nm**

## Excited States of Xanthophyll-Chlorophyll Dimers

**Excited States of Xanthophyll-Chlorophyll Dimers**

**cofacial arrangement**

- Zea-Chl

- Anthera-Chl

- Vio-Chl

- Andreas Dreuw
- Martin Head-Gordon

- Energy in eV

- Energy in eV

- Zea-Chl distance in Angstrom

- Anthera-Chl distance in Angstrom

- Energy in eV

- Vio-Chl distance in Angstrom

- S1

- CT

- S2

- ground state

- Qy

- CT

- ground state

- S1

- Qy

- Qx

- ground state

- CT

- S1

- Qy

- Qx

## Zeaxanthin-Chlorophyll Dimer

**LUMO**

**HOMO**

- Andreas Dreuw
- Martin Head-Gordon

## TA studies in the near-IR: Formation of the carotenoid radical cation.

- a **In **** PS II complexes from *****Synechocystis*****  PCC 6803 ****(Tracewell, C. A. et al.  (2003)  *****Biochemistry*****, 42, 9127).**

**          ****Spinach thylakoids**
**λ****Pump**** = 664 nm; ****λ****Probe**** = 1000 nm**

**Near-IR spectra**

**Difference kinetic indicates charge separations quenching during qE.**

## Near-IR Arabidopsis thaliana Studies 

**Difference Kinetic Fits**
- 		τrise(ps) 	         τdecay (ps)
- Detect 1000 nm
- WT	                            7.3                      210
*WT+ PsbS*		       6.7                      136
- Detect 540 nm
- WT	                              -	              ~ 7
*WT+ PsbS*		         -	              ~ 7

**Near-IR Arabidopsis thaliana Studies**
-                           (**λ****pump**** = 664 nm; ****λ****probe**** = 1000 nm****)**

**Time (ps)**

**Car****+****•**** formation is correlated with qE**

## One proposed quenching mechanism

**One proposed quenching mechanism**

**Gives rise to the positive signal at 1000 nm.**

**Corresponds to the negative (bleaching) signal in the 540 nm region.**

_**Assigned time constants**_

- kTr, kAdQ ~1/(100-300 ps).
**~1/(10 ps) **-** corresponds to the net Chl pool decay rate in the vicinity of the charge transfer complex.**

- kCS ~ 1/(100-300 fs).
- kRec ~1/(150 ps), corresponds to the recovery dynamics in visible and near-IR regions.
- gAnn ~ 1/[(10 ps)*n0], n0 – number of initial excitations in the complex.