The outstanding role of spermine in eliciting defense adaptation of soybean to different levels of water deficit (0, -0.1, -0.5 and -1.1 MPa) was investigated by determining the changes in growth, photosynthetic pigments, osmolytes, water relations, and antioxidants. All the studied traits clearly revealed cultivar-dependent variation in response to water deficit where cv. Giza 111 was tolerant and cv. Giza 21 was sensitive. Both cultivars came in agreement that photosynthetic limitation (chlorophylls reduction) was the troubling shot induced by water deficit. Such limitation was reflected on three directions (a) disturbances of water relations (stomatal conductance, transpiration rate, relative water content and water use efficiency), (b) down regulation of metabolites which affect osmotic adjustment and (c) elevated reactive oxygen species (increased hydrogen peroxide) and destruction of membrane stability (increment of …