Engineering Photosynthesis II: Energy Beyond the Rainbow Flashcards
1
Q
Structure
A
1.
2.
3.
2
Q
Light is not evenly distribution across the Earth’s surface
A
photon flux density varies across latitudes
3
Q
Where has photon flux density been measured
A
- equator
- Marrakesh
- Oxford
- Reykjavik
4
Q
Temperature is not evenly distributed across the Earth’s surface
A
annual average varies across latitudes
5
Q
light is scattered and absorbed by the atmosphere
A
- Rayleigh effect
- only certain wavelengths get through
6
Q
spectral intensity
A
- downgoing solar radiation: 70-75% transmitted
7
Q
UV
A
absorbed by O2 and ozone
8
Q
atmospheric component absorption
A
- GHGs produced by IR escape
9
Q
GHGs
A
- water vapour
- methane
- nitrous oxide
10
Q
absorption @ pigment level
A
- x2
- chlorophyll a and b
- only certain wavelengths of light can be used for photosynthesis
11
Q
light environment is
A
constantly fluctuating
12
Q
position in the canopy
A
- has a large effect on light levels
- shading: fraction of a s
13
Q
Which processes affect light absorption?
A
- latitude
- Rayleigh scattering
- atmospheric components
- pigments
- canopy position
- leaf angle
14
Q
leaf level
A
- leaves at the bottom don’t really respire
15
Q
plant growth artefact
A
- leaves shade the previous leaves they made
- leaves are semi-translucent (3/4 cells thick)
16
Q
chlorophyll
A
an alternating lattice of double and single bonds, resulting in a delocalised electron mass
17
Q
chlorophyll light interception results in
A
elevated energy state
18
Q
3 things can happen when chlorophyll intercepts light
A
i) fluorescence
ii) NPQ
iii) photosynthesis
- these processes are all under balance, and constantly fluctuating
19
Q
fluorescence
A
emit energy as light
20
Q
NPQ
A
- non-photochemical quenching
- emit energy as heat
21
Q
photosynthesis
A
- Forster resonance photochemical energy transformer
22
Q
light energy
A
used to make ATP, NADPH
23
Q
NAPDH
A
reducing power
24
Q
To fix one molecule of CO2 costs
A
- 3ATP
- 2NADPH
25
PSs
- photosystems
- light-absorbing complices
- x2
- channel high energy e-s
- site of photolysis
26
photolysis
- H+ can't cross membranes
- require ATP sythase
27
yield
- f(total amount of light energy harvested over the growing season)
- correlated with light energy capture and proton conversion
28
how much light energy is used/lost at each step?
- 14800GJ outside PAR
- 1420GJ reflected
- 1910GJ fluoresced
- 1660GJ NPQ
- 7110GJ photosynthesis
29
why do we need NPQ?
- excess light destroys D protein
- complex shredding requires refolding + insertion
- v. expensive, wasteful
30
D protein
- PSII
- constantly shredded
- highest turnover
- site of photolysis
- only ever lasts a few reactions
31
measuring NPQ
- PhiPSII
32
Three ways to improve light availability response
1) speed up RUBISCO reaction time
2) speed up NPQ reaction time
3) change canopy light absorption
33
it takes..
time to acclimate phtosynthesis to run at maximum speed
34
Setaria viridis
- fast reacting plant
- 500s to reach 90% maximum capacity in lower canopy leaves
- can we speed up the activation rate to increase yield?
- yes! engineer RUBISCO activase; faster induction kinetics
35
RUBISCO activase
- ATP-dependent
- relies on protons
- pulls off inhibitory mark
- lower conc. than RUBISCO itself
36
Hordeum vulgare RUBISCO activase oe
- faster activation
- decreased RUBISCO (higher turnover rate; damage)
- decreased photosynthetic rate
- decreased biomass and yield
37
Rice RUBISCO activase modification
- substantial natural variation in 14 different accessions: fast and slow activators
- we need a targeted breeding programme
38
NPQ
- switches on v quickly to dampen energy
- conservative; slow to switch off
- over-depletion on light cessation
39
What would happen if you could turn off NPQ faster?
- faster recovery
- faster photosynthetic rate
- more CO2 assimilation
- greater yield
40
Zeaxanthin violaxanthin cycle
- zeaxathin -(ZEP)-> violaxanthin
- violaxanthin -(VDE)-> zeaxanthin
- balance
- slow
- conversion is light-dependent
41
zeaxanthin
- polymer
- single and double bonds
- delocalised e- cloud accepts electrons from chlorophyll
42
ZEP
- zeaxanthin epoxidase
- speeds up NPQ relaxation
43
VDE
- violaxanthin de-epoxidase
44
PIIpS
- photosystem II protein S
- adjusts fast
45
increasing VDE?
- faster recovery
- increased net CO2 fixation rate (non-significant)
- may become significant when normalised across life-span
46
VDE, ZEP, PIIps oe
increased dry weight, plant height
47
changing light absorption in the canopy
- better spectral use
- expanding absorption bounds?
48
cyanobacteria
- chlorophyll a and b
- upper level
- endosymbiogenetic
- modern chloroplast
49
purple sulphur bacteria
- far-red absorbing chlorophylls
- lower level (anoxic)
- generated life on Europa
- props up ecosystems
- hydrothermal vents
50
chlorophyll d
- Cyanobacterial
- e.g. Acaryochloris marina
- red-shifted
- absorbs IR
51
LHCII
- main antenna protein of PSII
- light harvesting complex II
52
functional reconstitution of LHCII w/ chlorophyll d in vitro - set-up
i) made LHCII in E. coli
ii) extracted chlorophyll a and b from spinach
iii) extracted chlorophyll d from A. marina
iv) reconstituted LHCII w/ different chlorophyll mixtures: ab/db
53
functional reconstitution of LHCII w/ chlorophyll d in vitro - obs
- db could absorb far-red (700nm)
54
functional reconstitution of LHCII w/ chlorophyll d in vitro - next steps
in vivo
55
reduce chlorophyll content of all leaves
- individual leaves: lower photosynthetic rate
- canopy: higher light penetration
- same yield
