**5.5 GSH and GSSG determination**

Reduced glutathione and oxidized glutathione was measured by spectrophotometry (Beckman Instruments, Fullerton, CA) according to the method of Tietze (Tietze, 1969). Measurements with GSH concentrations bellow 200 μmol/g wet weight were excluded from calculation because of high possibility for error. Results were then weighted for hydroxyproline content and expressed as μmol/mg. Samples were run in duplicates and run according to supplier's instructions (OxisResearch, Portland, OR).
