Hi Janice,
The response by Subbaiah Chalivendra from Illinois was excellent, but
missed a couple of points. First the site of photorespiration is in the
chloroplasts, not in the mitochondria. Secondly, photorespiration does
not occur in the mesophyll cells of C4 plants because PEP carboxylase
has no affinity for oxygen and can only combine PEP with CO2 to produce
OAA. Photorespiration is supressed in the bundle sheath cells because
the levels of CO2 are much higher than in the mesophyll and Rubisco has
a 10 fold higher affinity for CO2 than it does for O2.
Gerry Deitzer
Department of Natural Resource Sciences
University of Maryland
College Park, MD 20742-4452
