8: Improving Photosynthesis - Light interception Flashcards
Structure of the lecture
- Issue 1: The light environment of Earth
- Issue 2: Inefficiency of photosynthesis
- Issue 3: The canopy
- Solution 1: Speeding up Rubisco
- Solution 2: Speeding up NPQ turn-off
- Solution 3: Changing absorption in canopy
How is the light distribution across Earth uneven?
1.1
Light and temperature are not evenly distributed across the surface of Earth due to its spherical nature.
Light is scattered and absorbed by the atmosphere (Rayleigh scattering)
Only certain wavelengths of light can get through the atmosphere
What are the 3 potential responses of a plant to light?
2.1
- Fluorescence (Dissipation of light as light)
- NPQ (Non-photochemical quenching. Light is dissipated as heat)
- PQ (Photochemical quenching). Light is used for photosynthesis via Forster resonance transer)
Where is light lost at different stages of photosynthesis?
2.2
- Light not actually absorbed by chlorophyll
- Light is reflected or transmitted
- Chlorophyll is inefficient
- NPQ
What is the importance of NPQ?
2.3
Excess light energy is dissipated via NPQ, in order to prevent damage of the D1 protein in PSII. As light energy increases, less and less of it will be used for photosynthesis, and more NPQ is needed to prevent damage.
What are the 3 main issues with light absorption in a plant canopy
3.1
- Height from top to bottom
- ‘Gear up’ time
- Lower leaves
How does height pose an issue in the plant canopy?
3.2
Large height difference between top and bottom of a plant, which limits light absorption possible. More light of appropriate wavelengths will be dissipated/reflected/wasted
How does ‘gear up time’ pose an issue in the plant canopy?
3.3
Photosynthesis takes around 400 seconds to ‘gear up’. Dappled light, or even dim light means that it takes a while to get to maximum photosynthesis, unless it has strong, constant light
How do lower leaves in a plant struggle in plant canopies?
3.4
Lower leaves struggle to access correct wavelengths, since has all been absorbed by higher canopies. Light will be more dappled/infrequent.
How would speeding up Rubisco acivation time improve light interception?
4.1
Increasing the levels of Rubisco activase (RA)
RA is required to cleave an inhibitory mark off Rubisco to allow it to respond to light
Several orders of magnitude less RA than Rubisco
More RA, the faster Rubisco could be activated. Acceleration of acclimation.
How has RA increase been tested?
4.2
Fukayama et al., 2012
Overexpression of barley RA in rice.
RA Plants appeared to respond faster to light than WT.
However, overall Rubisco content was lower, and biomass ended up being reduced and leading to smaller yield.
How can we increase the success of RA activation in the future?
4.3
- More testing on more different species.
- Plants testing in beneficial environments.
- Targeted breeding programmes to improve time and yield
How could speeding up NPQ reaction time improve light interception?
5.1
NPQ switches on very rapidly, but turns off very slowly. Improving turn-off time may allow for increase in biomass, since more light can be used for photosynthesis
What biological mechanisms can we manipulate to speed up NPQ reaction time?
5.2
Overexpression of VPZ state. VPZ is made up of 3 proteins: ZEP, VDE and Psbs
ZEP: Causes NPQ relaxation
VDE: Balances ZEP
Psbs: Ensures NPQ levels remain at WT level
More VPZ state = more photosynthesis per unit time = more biomass
How has relaxation of the NPQ state been tested for?
5.3
De Souza et al., 2022
20-30% increase in biomass in VPZ plants
Improvements in dry-weight, land area and plant height
