Hydrogen peroxide (H22) is a widely distributed small molecule involved in multiple signal pathways and developmental events.In the green plants, H2O2 are mainly produced during the process of photosynthesis, respiration, photorespiration and wound or pathogen triggered ROS burst.Most of these processes are mediated by oxidases using various substrates.Apart from the ROS burst which is mediated by membrane associated NADPH oxidases (rboh A~F family) under conditions of wounding and/or pathogen invasion, photorespiration constitutes the majority of H2O2 production in healthy mesophyll cells.The production of H2O2 during photorespiration is catalyzed by glycolate oxidase (GOX) in peroxisome, which oxidizes glycolate into glyoxylate by transferring one electron to O2 and oxidizes H2O into H2O2.In Arabidopsis, the GOX family genes can be categorized into 4 types, i.e.GOX1 a/b, GOX2 a/b, GOX3 and GOX4, based on sequence homology.Real time PCR results indicated that GOX1 a/b was the most highly expressed among the 4 types of GOX genes.