Engineering Photosynthesis I: Bypassing Respiration Flashcards
1
Q
Human pop growth
A
- 2050: 9-10bn
- average increase: c75mill/year; 1.1% (Germany)
2
Q
Consumption trends
A
- 2050: c3400kcal/person/day
- ^c15kcal/person/year; 0.6%
- 1/5th slice of bread
- 78 million loaves / day
- 2026: 15mill tonnes > wheat; 51,000km^2 (France)
- 2,340,000m^2 cows
3
Q
2050
A
We need to produce c70% more food
4
Q
Crop yield improvements
A
- have not kept pace w demand
- 1.1% since 1960/year
- 0.3% > land use/year
5
Q
Land use
A
- c15bn trees
- c30% GHGs
- CO2 release
- < biodiversity; intensive megafarms = ecological deserts
6
Q
Fun facts
A
- there are 10 more humans by mass than all wild animals combined
- 1/2 arable land on earth is farms
7
Q
We need to radically intensify
A
Food production / land area
8
Q
RUBISCO
A
- generated life from carbon
- Evolved: > CO2 (105,000ppm) , <O2 (10ppm)
- CO2 10,000x> O2
- 3.2Bya
9
Q
Now
A
- CO2: 400ppm
- O2: 210,000ppm (500x>)
10
Q
RUBSICO reactions
A
- both CO2 and O2 in separate reactions
- low CO2 specificity over O2
11
Q
RuBP + CO2 ->
A
3-PGA + 3-PGA
12
Q
RuBP + O2 ->
A
3-PGA + 2-PG
13
Q
Photorespiration
A
- RUBISCO is busy
- inherent costs
- more frequent due to higher O2
14
Q
Photolysis
A
- splits water into proton and oxygen using light
- oxygen producer
15
Q
Fixing CO2 is relatively cheap
A
3ATP + 2NADPH
16
Q
O2 fixing recovery is complicated and expensive
A
- 2-PG inhibits TPI, SBPase and PFK; need to get it out of the chloroplast and degrade it, quickly!
- 30-80% CO2 released for refixation (remainder used as glycine, serine)
- 50% released CO2 escapes back into atmosphere
- c5-10% NH4+ -> NH3 @ cytosolic pH (>10% of root uptake; needs refixing)
- NH3 escape = 5% N losses
17
Q
Environmental effects on photo respiration
A
- more frequent @ higher temperatures
- 30% CO2 fixation reduction
18
Q
RUBISCO Evolution
A
- very old
- constrained by multiple factors
- 1aa substitution every 7.2My
19
Q
Alternative solutions?
A
- CAM, C4
- O2:CO2
20
Q
Photorespiratory bypasses
A
1) GOC
2) Maurino
3) Ort
4) Peterhansel
21
Q
Common bypass themed
A
- cut 2-PG off from mitochondrial/peroxisome route
- liberate CO2 in chloroplast
- prevents C and N losses
22
Q
GOC bypass
A
1) 2-PG -PGP (-P)—> glycolate
2) glycolate -GO (O2->H2O2) -> oxalate
3) oxalate -OO (O2-> H2O2) -> 2CO2
23
Q
H2O2 -> O2
A
CAT
24
Q
GOC bypass output
A
For every RUBISCO oxygenation:
- 2CO2 released in chloroplast (no ammonium liberation)
- 6ATP, 4NADPH to refix CO2
25
Is a bypass working?
Measure normal plant w bypass at low and normal levels of oxygen
26
GOC bypass assessment
- 19% increase in ambient O2 photosynthesis
- same increase when O2 small
- methodological error
27
Maurino bypass
1. 2-PG -PGP (-P) -> glycolate
2. Glycolate -GO (O2->H2O2) -> glyoxylate
3. Glyoxylate -MS-> malate
4. Malate -ME (NADP-> NADPH) -> pyruvate + CO2
5. Pyruvate -PD (NAD-> NADH; CoA-> acetyl-CoA)-> CO2
28
Maurino bypass output
For every RUBISCO oxygenation:
1. 1NADH
2. 1NADPH
3. 2CO2
4. No ammonium liberation
5. 6ATP + 4NADPH to refix CO2
29
Maurino bypass assessment
No significant increase at ambient CO2
30
Ort bypass
1. 2-PG -PGP (-P) -> glycolate
2. Glycolate -GDH (NAD->NADH) -> glyoxylate
3. Glyoxylate -MS-> malate
4. Malate -ME (NADP-> NADPH) -> pyruvate + CO2
5. Pyruvate -PD (NAD-> NADH; CoA-> acetyl-CoA)-> CO2
31
Ort bypass output
- 2NADH
- 1NADPH
- 2CO2
- no ammonium liberated
- 6ATP, 4NADPH to refix
32
Ort bypass
C30% increase in both
33
Peterhansel pathway
1. 2x 2-PG -PGP (-P) -> glycolate
2. Glycolate -GD (NAD-> NADH) -> glyoxylate
3. 2x glyoxylate = tartronic semialdehyde
4. tartronic semialdehyde -GK (ATP-> ADP) -> glycerate
5. Glycerate -(ATP->ADP)-> 3-PGA -> CBC
34
Peterhansel pathway output
For every 2x 2-PG:
1. 1x ATP consumed
2. 1x NADH generated
3. 1x CO2 released
4. No ammonium liberation
5. 3ATP, 2NADPH to refix CO2
35
Peterhansel assessment
- c50% ^
36
Camelina sativa
- peterhansel
- not commercialised : GMO
37
Living carbon
- poplar
- Ort
- commercialised
- smol >
