7: Improving photosynthesis - Photorespiration Flashcards
Structure of the lecture
- The issue: Increasing crop yield
- Current status: How are attempts going?
- A focal point: Photorespiration
- Improvements to photorespiration
What are the 3 main needs to increase crop yield?
1.1
- Dramatic changes in land-use
- Dramatic increase in human population
- Rising food consumption
How has/is land-use changing over time?
1.2
Land-use has dramatically changed since the industrial revolution, and continues to do so. This change is driven by the Haber-Bosch process, the improvement of machinery and genetic technologies.
How has/is human population changing over time?
1.3
Human population is dramatically rising. Projected to reach 9-10 billion by 2050. All of these individuals have the right to high quality nutrition. 1.1% annual increase in population size.
How was/is food consumption changing over time?
1.4
Food consumption is rising by an average of ~15 daily kcal per year. Predicted to be 3400 kcal per person by 2050.
By how much do we need to increase food production?
1.5
Roughly 70% more food is required across Earth by 2050 due to increase population size, land-use and nutritional requirements
How are current attempts to meet crop demand going?
2.1
- 50% of all arable land currently being farmed.
- More than 500 timess more livestock on Earth than wild mammals.
- 15 billion trees cut down annually. Leading to 30% of global emissions.
What is photorespiration?
3.1
A wasteful process in which Rubisco oxygenated RuBP, and lowers the efficiency of photosynthesis. It has the cost of 6ATP, 1 NADPH and re-fixed NH4+
Why does photorespiration negatively impact plants?
3.2
- Complex and energy-expensive.
- Results in loss of CO2 and NH4+, which need to be recaptured
- Results in 30% decrease in CO2 fixation at high CO2 levels
How is the Rubisco enzyme mal-adapted for modern photosynthesis?
3.3
Rubisco evolves exceptionally slowly, and photorespiration is not appropriate for current carbon levels.
Rubisco is made from 8 tertiary chains, and a number of cofactors, meaning that the accumulation of beneficial mutations is slow
Only one amino acid substitution every 7.2 million years
What are the four main methods to reduce photorespiration (ranked)?
4.1
- Peterhansel
- Ort
- Maurino
- GOC
What is the main, over-arching idea of how to overcome photorespiration?
4.2
Trying to bypass the process of photorespiration via the peroxisome and mitochondria, in order to avoid the complex biochemitry of the chloroplast
Describe the pros/cons of the Peterhansel pathway
4.3
Most effective pathway
Cost: 2 ATP, 1.5 NADPH
O2: None
H2O2: None
CO2: 1
NADH: 2
Ambient CO2: 50% increase
High CO2: No change
Describe the pros/cons of the Ort pathway
4.4
More favourable than Maurino or GOC
Cost: 6 ATP, 1.5 NADPH
O2: None
H2O2: None
CO2: 2
NADH: 2
Ambient CO2: 30% increase
High CO2: Unusual results. We may well not be bypassing photorespiration. Other mechanism
Describe the pros/cons of the Maurino pathway
4.5
Energetically favourable
Cost: 6 ATP, 2 NADPH
O2: None
H2O2: None
CO2: 2
NADH: 1
Ambient CO2: No change
High CO2: Untested
