Earth & Environmental Science Journalism:

Science Research Project

The Effects of Photorespiration on Mitochondrial Respiration in the Light:

Kok Effect Measurements in C3 and C4 Salt Marsh Grass Species.

Emily Muhlhausen

Salt Marsh Site
Spartina Patens Scirpus Olneyi


Photorespiration is a possible cause of the inhibition of respiration in the light (RL) demonstrated by the Kok effect.  Products of photorespiration could potentially deactivate a key respiratory enzyme – the pyruvate dehydrogenase complex (PDC). By comparing the results of Kok method light response curves under conditions where photorespiration is and is not likely to occur, this study attempts to isolate the role of photorespiration in the photoinhibition of RL. Comparative measurements were taken between a C3 and a C4 species and at ambient (385 ppm) and elevated (800 ppm) CO2 concentrations. 10 samples were measured of each of two salt marsh grass species; Scirpus olneyi, a C3 plant; and Spartina patens, a C4 plant. Statistical analyses indicate that the mean RL/RD ratio was significantly lower  for the C3 plants at ambient CO2 concentrations. The Kok effect was  not present (or was extremely reduced) in the C3 species at an  elevated CO2 concentration and the C4 species at either CO2 level.  This study presents evidence in support of the hypothesis that  photorespiration indirectly causes the photoinhibition of respiration.

  Research Site - Smithsonian Environmental Resarch Center, Chesapeake Bay, MD  



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Last updated: 8 January 2001, KAK.