The oxidative tress provoked by water stress had a direct effec to proper PSII function. The Fv/Fo parameter, a sensitive Chl fluorescence ratio is related to the maximum quantum yield of PSI Iphotochemistry (Babani and Lichtenthaler, 1996). A decline in Fv/Fo indicates a disturbance or damage of the photosynthetic apparatus,and has been frequently used as an indicator of photoinhibition (Calatayud et al., 2004).