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Re: [APD] high O2 levels does promote free radical formation
>O2 isn't going to do anything, as you discovered. You need the free O-
High oxidation levels does promote radical formation. High DO levels promotes photorespiration which produces H2O2.
A seemingly wasteful process of breaking down RuBP, associated with consumption of O2 and release of CO2
This process is distinct from oxidative phosphorylation: called photorespiration.
At low [CO2] and high [O2], photorespiration can outdo photosynthesis rate.
We generally have high CO2 as well, but I tested that and found no difference in production rates.
The first stage of photorespiration is catalyzed by Rubisco also. This is responsible for the "oxygenase" part of the Rubisco name, George Bowes discovered this, one of my past professors, he worked mainly with an alga.
Chemistry is somewhat similar to carboxylase reaction:
RuBP + O2 -> CH2OPO3 2-HCOH-COO- + CH2OPO3 2- -COO-
The products are 3-PG CH2OPO3 2- HCOH-COO- and 2-phosphoglycolate CH2OPO3 2- COO-
In air, carboxylation/oxygenation ratio is between 2.5 and 3
Photorespiration lowers efficiency of photosynthetic carbon fixation from 90% to about 50%
Photorespiration is also associated with consumption of ATP and NADH,
they are used in the attempt to recover part of the fixed carbon in photorespiratory carbon oxidation cycle (PCO cycle) PCO cycle involves 4 compartments: chloroplast, cytoplasm, peroxisome(absent in some algae but they have similar pathways) and mitochondrion
Further transformations of 2-phosphoglycolate:
gets dephosphorylated by 2-phosphoglycolate phosphatase in the chloroplast into glycolate:
CH2OPO32-COO- -> CH2OH-COO- + P Glycolate
exported into cytoplasm and when to peroxisome
in peroxisome and mitochondrion, oxidized to CO2
Glycolate oxidase catalyzes oxidation of glycolate by molecular oxygen to glyoxylate (alcohol into aldehyde):
CH2OH-COO- + O2 -> COH-COO- + H2O2
Oxygen is reduced into hydrogen peroxide: potentially dangerous (can lead to free radicals)->catalase breaks down into H2O and O2
Therefore high O2 levels can over load the plant and algae's protection by the production of H2O2. PR is a well documented process and basic stuff for plant physiology course work.
So is PR significant in reducing algae?
The issue is the amount of free radicals produced. Even at the highest DO levels we see in our tanks, O2 is not the reason for the decline in algae. That's what the test I did showed.
So we can rule out why algae does not grow in a well run planted with high DO levels.
What H2O2 does is fairly straight forward. You overload the smaller organisms abilty to process these radicals. Leave a plant in there long enough, you'll roast it also.
Like a drug, too much kills the patient, too little has no effect.
Adding a shock load of H2O2, kills plants also, not just algae if you add too much and with finer leaves, same it true for bleach dips etc.
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