S-deficiency and/or S-deprivation decreases the cell sap osmotic potential resulting from a net increase of intracellular solutes rather than from a loss of cell water and chlorophyll content resulting in a restriction of Rubisco synthesis and provoked the chlorosis of young leaves (Lee et al., 2014; Muneer et al., 2014). These imply that S-deficiency results in a general inhibition of photosynthesis and protein synthesis. On the other hand, several studies have indicated that S nutrition has a potential role in stress tolerance and defense mechanism. Sulfur is an essential element in the formation of sulfhydryl (S-H) and disulphide bond (S-S). These bonds are important for the stabilization of protein structures. In this context, the roles of S nutrition in alleviating negative responses to salinity stress (Fatma et al., 2014) and iron deficiency (Muneer et al., 2014) have been widely reported. In this study, we hypothesized that cultivar variation in sulfur use efficiency (SUE) under Polyethylene glycol (PEG)-induced water stress may be attributed to S-uptake efficiency (SUpE; S uptake per S supplied), and that the genotype having higher SUE is more tolerant to PEG-induced water stress. To test this hypothesis, direct quantifications of S uptake was done by a 34S tracing method. The responses of photosynthetic activity-related parameters to PEG-induced water stress were also assessed in relation to SUE in two B. napus cultivars
