Measuring carbon fixation:
- Not so easy because mitochondria are evolving, producing CO2.
- CO2 fixation rate, how much is actually fixed.
- Micromoles carbon per cell per minute is how you measure this rate.
- CO2 fixation in the dark, photosynthesis is off, below zero. Only thing your
measuring is rate of mitochondrial respiration, which produces carbon.
- In room light: increase in fixation, linear increase in rate with more exposure
- More light, more photochemistry is reaction center in PS2.
- More of the NADPH and ATP that you need to fixate to. As you generate more
products of light reactions to be consumed in Calvin cycle, Calvin cycles can
turn faster and fix more CO2.
- Rate of Calvin cycle is directly proportional to products of light reactions.
- Won’t keep going up with increase light because the enzymes in Calvin cycle
can’t work any faster than their maximum rate. Can have many reactants but
Calvin cycle will still go at it’s set maximum speed.
- The rate will plateau.
- Turnover rate of enzymes, regeneration of RuBP can control rate. The speed
at which this happens.
- Inhibition with oxygen. - Carbon dioxide can control rate, if given more CO2 maybe rate would
- Any light added past saturation point is excess light.
- P680 is bound by protein, that protein breaks down very quickly, when
above light saturation, absorbing more light than can use, P680 very reactive.
Proteins in photosystem susceptible to being broken down.
- Curve is net, anything below means evolving more CO2 than bringing in.
- To grow, plant must gain carbon, if at light below 0, releasing more CO2 than
using. Losing more than gaining.
- Perfect light intensity: rate of CO2 being used and rate of CO2 released is
even. Light compensation point. Light can compensate for amount of CO2
- For a healthy plant you want to be above light compensation point.
- Different plants have different light compensation points.
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