light-dependent oxygen consumption

Kathleen Archer Kathleen.Archer at
Fri Jun 7 07:37:54 EST 2002

Dear Plant Ed Friends,
I have been working with isolated pea chloroplasts, and have observed a 
puzzling thing that I hope one of you out there can explain.  When we 
provide the chloroplasts (purified on Percoll density gradients, which
been shown to separate chloroplasts from other cell organelles) 
with  buffered sodium bicarbonate (5 mM) and attempt to measure 
CO2-dependent oxygen evolution (Clark-type electrode), what we get is 
light-dependent oxygen consumption.  If we turn off the lights, the
in the chamber remains steady, if we turn on the lights, oxygen is 
consumed.  We have tested our system with leaf strips, which behave as
would anticipate and generate a nice increase in oxygen in the light, so
think our setup is ok.

The only thing I can think of is photorespiration, but I expect to see
only when CO2-dependent photosynthesis is running.  Actually, I don't 
expect to see it because presumably at the generous levels of CO2
oxygen production should swamp out any oxygen consumed by the 
photorespiratory pathway, so I really don't know how to explain this. 
Thanks for your help,
Kathleen Archer

Kathleen Archer
Dept. Biology
Trinity College
Hartford, CT 06106
Ph: (860)297-2226
kathleen.archer at


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