The substrate of Photorespiration is:

 a) Glycolate
 b) Pyruvic acid
 c) Fructose
 d) Glucose

SSC CGL-15

Glycolate. The oxygen sensitivity of glycolate-stimulated CO2 production was found to be compatible with the proposal that glycolate is a substrate of photorespiration. Source:http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1086949/