Seed germination is an important growth phase in the plant life cycle that can be injured by osmotic stress. Germination is divided into three phases and many processes are initiated before radical protrusion. Many metabolic activities occur, especially in Sensu stricto germination phase since the seed embryo is a live organ, so differences in protein patterns are important in this phase. This study was carried out to find out the effects of osmotic stress on protein patterns in Sensu stricto germination phase. Effects of osmotic stress (-12 bar) on T. aestivum embryo (Sardari and Qods, tolerant and susceptible cultivars, respectively) proteins were evaluated. An osmotic potential of -12 bar was selected as the critical stress level, because at this treatment, germination percentage in susceptible cultivar was too low, but in tolerant cultivar was 50% as compared to control condition. Osmotic stress decreased germination percentage and caused adverse effects on protein patterns. After 2-DE proteome analysis of wheat embryo axis, 1000 spots were reproducible, although 16 spots were expressed differentially. Five protein categories were identified by MALDI-TOF/TOF in 16 differentially expressed, including energy (19%), stress/disease /defense (25%), metabolism (37%), protein synthesis/degradation (13%), and signal transduction (6%). Therefore, it should be noted that seeds were acting as intelligent systems which has an important role in response mechanism to osmotic stress during germination, especially before radical protrusion. In this study, it was demonstrated that stress and metabolism-related proteins such as HSPs, 1–Cys peroxiredoxin, alpha amylase inhibitor, and ADP–glucose pyrophosphorylase were more than other protein classes had vital roles in response to osmotic stress at 24 HAI. The results indicated that protein abundance under osmotic stress depends on the severity and amount of stress and imbibition time.

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