Engineering Photosynthesis I: Bypassing Respiration Flashcards
Human pop growth
- 2050: 9-10bn
- average increase: c75mill/year; 1.1% (Germany)
Consumption trends
- 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
2050
We need to produce c70% more food
Crop yield improvements
- have not kept pace w demand
- 1.1% since 1960/year
- 0.3% > land use/year
Land use
- c15bn trees
- c30% GHGs
- CO2 release
- < biodiversity; intensive megafarms = ecological deserts
Fun facts
- there are 10 more humans by mass than all wild animals combined
- 1/2 arable land on earth is farms
We need to radically intensify
Food production / land area
RUBISCO
- generated life from carbon
- Evolved: > CO2 (105,000ppm) , <O2 (10ppm)
- CO2 10,000x> O2
- 3.2Bya
Now
- CO2: 400ppm
- O2: 210,000ppm (500x>)
RUBSICO reactions
- both CO2 and O2 in separate reactions
- low CO2 specificity over O2
RuBP + CO2 ->
3-PGA + 3-PGA
RuBP + O2 ->
3-PGA + 2-PG
Photorespiration
- RUBISCO is busy
- inherent costs
- more frequent due to higher O2
Photolysis
- splits water into proton and oxygen using light
- oxygen producer
Fixing CO2 is relatively cheap
3ATP + 2NADPH
O2 fixing recovery is complicated and expensive
- 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
Environmental effects on photo respiration
- more frequent @ higher temperatures
- 30% CO2 fixation reduction
RUBISCO Evolution
- very old
- constrained by multiple factors
- 1aa substitution every 7.2My
Alternative solutions?
- CAM, C4
- O2:CO2
Photorespiratory bypasses
1) GOC
2) Maurino
3) Ort
4) Peterhansel
Common bypass themed
- cut 2-PG off from mitochondrial/peroxisome route
- liberate CO2 in chloroplast
- prevents C and N losses
GOC bypass
1) 2-PG -PGP (-P)—> glycolate
2) glycolate -GO (O2->H2O2) -> oxalate
3) oxalate -OO (O2-> H2O2) -> 2CO2
H2O2 -> O2
CAT
GOC bypass output
For every RUBISCO oxygenation:
- 2CO2 released in chloroplast (no ammonium liberation)
- 6ATP, 4NADPH to refix CO2
Is a bypass working?
Measure normal plant w bypass at low and normal levels of oxygen
GOC bypass assessment
- 19% increase in ambient O2 photosynthesis
- same increase when O2 small
- methodological error
Maurino bypass
- 2-PG -PGP (-P) -> glycolate
- Glycolate -GO (O2->H2O2) -> glyoxylate
- Glyoxylate -MS-> malate
- Malate -ME (NADP-> NADPH) -> pyruvate + CO2
- Pyruvate -PD (NAD-> NADH; CoA-> acetyl-CoA)-> CO2
Maurino bypass output
For every RUBISCO oxygenation:
1. 1NADH
2. 1NADPH
3. 2CO2
4. No ammonium liberation
5. 6ATP + 4NADPH to refix CO2
Maurino bypass assessment
No significant increase at ambient CO2
Ort bypass
- 2-PG -PGP (-P) -> glycolate
- Glycolate -GDH (NAD->NADH) -> glyoxylate
- Glyoxylate -MS-> malate
- Malate -ME (NADP-> NADPH) -> pyruvate + CO2
- Pyruvate -PD (NAD-> NADH; CoA-> acetyl-CoA)-> CO2
Ort bypass output
- 2NADH
- 1NADPH
- 2CO2
- no ammonium liberated
- 6ATP, 4NADPH to refix
Ort bypass
C30% increase in both
Peterhansel pathway
- 2x 2-PG -PGP (-P) -> glycolate
- Glycolate -GD (NAD-> NADH) -> glyoxylate
- 2x glyoxylate = tartronic semialdehyde
- tartronic semialdehyde -GK (ATP-> ADP) -> glycerate
- Glycerate -(ATP->ADP)-> 3-PGA -> CBC
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
Peterhansel assessment
- c50% ^
Camelina sativa
- peterhansel
- not commercialised : GMO
Living carbon
- poplar
- Ort
- commercialised
- smol >