Basic plant research lays the foundation to our understanding of plant adaptation to changing environmental conditions. Abiotic stress conditions generally disturb redox homeostasis and induce oxidative stress, which activates signaling pathways and adapt ive responses. This proposal focuses on the role of plant peroxisomes in detoxification and signaling of reactive oxygen species (ROS) in plants. The Reumann group has recently identified the two last members of the ascorbate-glutathione (ASC-GSH) cycle o f plant peroxisomes. Redox equivalent for glutathione recycling are hypothesized in the literature to be provided by the peroxisomal oxidative pentose phosphate pathway (OPPP) but experimental support is yet lacking. The German von Schaewen group has rece ntly identified specific isoforms of all three enzymes of the OPPP that are targeted to peroxisomes in vivo. Two young research groups with complementary expertise in metabolism of plant peroxisomes (Reumann group, Stavanger, Norway) and oxidative stress (von Schaewen group, Muenster, Germany) will merge their theoretical and practical expertise to investigate how plants cope with oxidative stress. We propose to resolve within the frame of a 2-year Norwegian-German collaboration how the peroxisomal ASC-GS H cycle and the OPPP are coordinated to provide sufficient redox equivalents for ROS detoxification. During four 3-4 week research visits the two groups will exchange PhD students, a postdoctoral fellow, and valuable expertise and coordinate their researc h activities. The research data will yield significant insights into yet unknown mechanisms how plants cope with oxidative stress caused by changing environmental conditions such as global warming and ultimately allow genetic engineering of crops to optim ize their stress tolerance.